diff --git a/.gitignore b/.gitignore
index 924afc1..5412b1c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -13,3 +13,6 @@ Gemfile.lock
 
 # rspec failure tracking
 .rspec_status
+
+# ruby version
+.ruby-version
\ No newline at end of file
diff --git a/firebase-admin-sdk.gemspec b/firebase-admin-sdk.gemspec
index d1e2632..cb21f0a 100644
--- a/firebase-admin-sdk.gemspec
+++ b/firebase-admin-sdk.gemspec
@@ -24,6 +24,7 @@ Gem::Specification.new do |spec|
   spec.add_runtime_dependency "googleauth", "> 0.16", "< 2.0"
   spec.add_runtime_dependency "faraday", "> 1", "< 3"
   spec.add_runtime_dependency "jwt", ">= 1.5", "< 3.0"
+  spec.add_runtime_dependency "google-apis-fcm_v1", ">= 0.19.0", "< 1.0"
 
   spec.add_development_dependency "rake"
   spec.add_development_dependency "rspec"
@@ -31,5 +32,5 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency "fakefs"
   spec.add_development_dependency "climate_control"
   spec.add_development_dependency "standard"
-  spec.add_development_dependency "activesupport"
+  spec.add_development_dependency "activesupport", "~> 7.0.8"
 end
diff --git a/lib/firebase-admin-sdk.rb b/lib/firebase-admin-sdk.rb
index eb5d864..281c622 100644
--- a/lib/firebase-admin-sdk.rb
+++ b/lib/firebase-admin-sdk.rb
@@ -34,4 +34,6 @@
 require_relative "firebase/admin/messaging/multicast_message"
 require_relative "firebase/admin/messaging/error_info"
 require_relative "firebase/admin/messaging/topic_management_response"
+require_relative "firebase/admin/messaging/send_response"
+require_relative "firebase/admin/messaging/batch_response"
 require_relative "firebase/admin/messaging/client"
diff --git a/lib/firebase/admin/messaging/aps.rb b/lib/firebase/admin/messaging/aps.rb
index 03410c4..a6b26e1 100644
--- a/lib/firebase/admin/messaging/aps.rb
+++ b/lib/firebase/admin/messaging/aps.rb
@@ -3,7 +3,7 @@ module Admin
     module Messaging
       # Aps dictionary to be included in an APNS payload.
       class APS
-        # @return [APSAlert, String, nil]
+        # @return [Firebase::Admin::Messaging::APSAlert, String, nil]
         #   Alert to be included in the message.
         attr_accessor :alert
 
@@ -12,7 +12,7 @@ class APS
         #   remain unchanged.
         attr_accessor :badge
 
-        # @return [String, CriticalSound, nil]
+        # @return [Firebase::Admin::Messaging::CriticalSound, String, nil]
         #   Sound to be played with the message.
         attr_accessor :sound
 
@@ -39,12 +39,12 @@ class APS
 
         # Initializes an {APS}.
         #
-        # @param [APSAlert, String, nil] alert
+        # @param [Firebase::Admin::Messaging::APSAlert, String, nil] alert
         #   Alert to be included in the message (optional).
         # @param [Integer, nil] badge
         #   Badge to be displayed with the message (optional).
         #   Set to 0 to remove the badge. When not specified, the badge will remain unchanged.
-        # @param [String, CriticalSound, nil] sound
+        # @param [Firebase::Admin::Messaging::CriticalSound, String, nil] sound
         #   Sound to be played with the message (optional).
         # @param [Boolean, nil] content_available
         #   Specifies whether to configure a background update notification (optional).
diff --git a/lib/firebase/admin/messaging/batch_response.rb b/lib/firebase/admin/messaging/batch_response.rb
new file mode 100644
index 0000000..4183f7c
--- /dev/null
+++ b/lib/firebase/admin/messaging/batch_response.rb
@@ -0,0 +1,29 @@
+module Firebase
+  module Admin
+    module Messaging
+      # The response received from a batch request
+      class BatchResponse
+        # The list of responses (possibly empty).
+        # @return [Array<SendResponse>]
+        attr_reader :responses
+
+        # The number of successful messages.
+        # @return [Integer]
+        attr_reader :success_count
+
+        # The number of failed messages.
+        # @return [Integer]
+        attr_reader :failure_count
+
+        # A response received from a batch request.
+        #
+        # @param [Array<SendResponse>] responses
+        def initialize(responses:)
+          @responses = responses
+          @success_count = responses.count(:success?)
+          @failure_count = responses.count - @success_count
+        end
+      end
+    end
+  end
+end
diff --git a/lib/firebase/admin/messaging/client.rb b/lib/firebase/admin/messaging/client.rb
index 61beada..afc34fa 100644
--- a/lib/firebase/admin/messaging/client.rb
+++ b/lib/firebase/admin/messaging/client.rb
@@ -1,3 +1,5 @@
+require "google-apis-fcm_v1"
+
 module Firebase
   module Admin
     module Messaging
@@ -5,8 +7,11 @@ module Messaging
       class Client
         def initialize(app)
           @project_id = app.project_id
-          @http_client = Firebase::Admin::Internal::HTTPClient.new(credentials: app.credentials)
+          @project_path = "projects/#{app.project_id}"
           @message_encoder = MessageEncoder.new
+          @http_client = Firebase::Admin::Internal::HTTPClient.new(credentials: app.credentials)
+          @service = Google::Apis::FcmV1::FirebaseCloudMessagingService.new
+          @service.authorization = app.credentials
         end
 
         # Sends a message via Firebase Cloud Messaging (FCM).
@@ -19,13 +24,10 @@ def initialize(app)
         #
         # @return [String] A message id that uniquely identifies the message.
         def send_one(message, dry_run: false)
-          body = {
-            validate_only: dry_run,
-            message: @message_encoder.encode(message)
-          }
-          res = @http_client.post(send_url, body, FCM_HEADERS)
-          res.body["name"]
-        rescue Faraday::Error => e
+          body = encode_message(message, dry_run: dry_run)
+          res = @service.send_message(@project_path, body, options: {skip_serialization: true})
+          res.name
+        rescue Google::Apis::Error => e
           raise parse_fcm_error(e)
         end
 
@@ -39,7 +41,21 @@ def send_one(message, dry_run: false)
         #
         # @return [BatchResponse] A batch response.
         def send_all(messages, dry_run: false)
-          raise NotImplementedError
+          raise "messages must be an Array" unless messages.is_a?(Array)
+          raise "messages must not contain more than 500 elements" unless messages.length < 500
+
+          responses = []
+          @service.batch do |service|
+            options = {skip_serialization: true}
+            messages.each do |message|
+              body = encode_message(message, dry_run: dry_run)
+              service.send_message(@project_path, body, options: options) do |res, err|
+                wrapped_err = parse_fcm_error(err) unless err.nil?
+                responses << SendResponse.new(message_id: res&.name, error: wrapped_err)
+              end
+            end
+          end
+          BatchResponse.new(responses: responses)
         end
 
         # Sends the given multicast message to all tokens via Firebase Cloud Messaging (FCM).
@@ -124,9 +140,9 @@ def make_topic_mgmt_request(tokens, topic, operation)
           TopicManagementResponse.new(res)
         end
 
-        # @param [Faraday::Error] err
+        # @param [Google::Apis::Error] err
         def parse_fcm_error(err)
-          msg, info = parse_platform_error(err.response_status, err.response_body)
+          msg, info = parse_platform_error(err.status_code, err.body)
           return err if info.empty?
 
           details = info["details"] || []
@@ -153,10 +169,19 @@ def parse_platform_error(status_code, body)
           [msg, details]
         end
 
+        # Encodes a send message request.
+        def encode_message(message, dry_run:)
+          body = {
+            message: @message_encoder.encode(message),
+            validateOnly: dry_run
+          }
+          JSON.generate(body)
+        end
+
         FCM_HOST = "https://fcm.googleapis.com"
         FCM_HEADERS = {"X-GOOG-API-FORMAT-VERSION": "2"}
         IID_HOST = "https://iid.googleapis.com"
-        IID_HEADERS = {"access_token_auth" => "true"}
+        IID_HEADERS = {access_token_auth: "true"}
 
         FCM_ERROR_TYPES = {
           "APNS_AUTH_ERROR" => ThirdPartyAuthError,
diff --git a/lib/firebase/admin/messaging/message_encoder.rb b/lib/firebase/admin/messaging/message_encoder.rb
index 7756b51..746b170 100644
--- a/lib/firebase/admin/messaging/message_encoder.rb
+++ b/lib/firebase/admin/messaging/message_encoder.rb
@@ -1,3 +1,5 @@
+require "json"
+
 module Firebase
   module Admin
     module Messaging
@@ -6,7 +8,7 @@ class MessageEncoder
         #
         # @param [Message] message
         #   The message to encode.
-        # @return [Hash]
+        # @return [String] A json encoded string.
         def encode(message)
           raise ArgumentError, "message must be a Message" unless message.is_a?(Message)
           result = {
@@ -17,7 +19,7 @@ def encode(message)
             notification: encode_notification(message.notification),
             token: check_string("Message.token", message.token, non_empty: true),
             topic: check_string("Message.topic", message.topic, non_empty: true),
-            fcm_options: encode_fcm_options(message.fcm_options)
+            fcmOptions: encode_fcm_options(message.fcm_options)
           }
           result[:topic] = sanitize_topic_name(result[:topic])
           result = remove_nil_values(result)
@@ -47,13 +49,13 @@ def encode_android(v)
           return nil unless v
           raise ArgumentError, "Message.android must be an AndroidConfig." unless v.is_a?(AndroidConfig)
           result = {
-            collapse_key: check_string("AndroidConfig.collapse_key", v.collapse_key),
+            collapseKey: check_string("AndroidConfig.collapse_key", v.collapse_key),
             data: check_string_hash("AndroidConfig.data", v.data),
             notification: encode_android_notification(v.notification),
             priority: check_string("AndroidConfig.priority", v.priority, non_empty: true),
-            restricted_package_name: check_string("AndroidConfig.restricted_package_name", v.restricted_package_name),
+            restrictedPackageName: check_string("AndroidConfig.restricted_package_name", v.restricted_package_name),
             ttl: encode_duration("AndroidConfig.ttl", v.ttl),
-            fcm_options: encode_android_fcm_options(v.fcm_options)
+            fcmOptions: encode_android_fcm_options(v.fcm_options)
           }
           result = remove_nil_values(result)
           if result.key?(:priority) && !%w[normal high].include?(result[:priority])
@@ -71,49 +73,49 @@ def encode_android_notification(v)
 
           result = {
             body: check_string("AndroidNotification.body", v.body),
-            body_loc_key: check_string("AndroidNotification.body_loc_key", v.body_loc_key),
-            body_loc_args: check_string_array("AndroidNotification.body_loc_args", v.body_loc_args),
-            click_action: check_string("AndroidNotification.click_action", v.click_action),
+            bodyLocKey: check_string("AndroidNotification.body_loc_key", v.body_loc_key),
+            bodyLocArgs: check_string_array("AndroidNotification.body_loc_args", v.body_loc_args),
+            clickAction: check_string("AndroidNotification.click_action", v.click_action),
             color: check_color("AndroidNotification.color", v.color, allow_alpha: true, required: false),
             icon: check_string("AndroidNotification.icon", v.icon),
             sound: check_string("AndroidNotification.sound", v.sound),
             tag: check_string("AndroidNotification.tag", v.tag),
             title: check_string("AndroidNotification.title", v.title),
-            title_loc_key: check_string("AndroidNotification.title_loc_key", v.title_loc_key),
-            title_loc_args: check_string_array("AndroidNotification.title_loc_args", v.title_loc_args),
-            channel_id: check_string("AndroidNotification.channel_id", v.channel_id),
+            titleLocKey: check_string("AndroidNotification.title_loc_key", v.title_loc_key),
+            titleLocArgs: check_string_array("AndroidNotification.title_loc_args", v.title_loc_args),
+            channelId: check_string("AndroidNotification.channel_id", v.channel_id),
             image: check_string("AndroidNotification.image", v.image),
             ticker: check_string("AndroidNotification.ticker", v.ticker),
             sticky: v.sticky,
-            event_time: check_time("AndroidNotification.event_time", v.event_time),
-            local_only: v.local_only,
-            notification_priority: check_string("AndroidNotification.priority", v.priority, non_empty: true),
-            vibrate_timings: check_numeric_array("AndroidNotification.vibrate_timings", v.vibrate_timings),
-            default_vibrate_timings: v.default_vibrate_timings,
-            default_sound: v.default_sound,
-            default_light_settings: v.default_light_settings,
-            light_settings: encode_light_settings(v.light_settings),
+            eventTime: check_time("AndroidNotification.event_time", v.event_time),
+            localOnly: v.local_only,
+            notificationPriority: check_string("AndroidNotification.priority", v.priority, non_empty: true),
+            vibrateTimings: check_numeric_array("AndroidNotification.vibrate_timings", v.vibrate_timings),
+            defaultVibrateTimings: v.default_vibrate_timings,
+            defaultSound: v.default_sound,
+            defaultLightSettings: v.default_light_settings,
+            lightSettings: encode_light_settings(v.light_settings),
             visibility: check_string("AndroidNotification.visibility", v.visibility, non_empty: true),
-            notification_count: check_numeric("AndroidNotification.notification_count", v.notification_count)
+            notificationCount: check_numeric("AndroidNotification.notification_count", v.notification_count)
           }
           result = remove_nil_values(result)
 
-          if result.key?(:body_loc_args) && !result.key?(:body_loc_key)
+          if result.key?(:bodyLocArgs) && !result.key?(:bodyLocKey)
             raise ArgumentError, "AndroidNotification.body_loc_key is required when specifying body_loc_args"
-          elsif result.key?(:title_loc_args) && !result.key?(:title_loc_key)
+          elsif result.key?(:titleLocArgs) && !result.key?(:titleLocKey)
             raise ArgumentError, "AndroidNotification.title_loc_key is required when specifying title_loc_args"
           end
 
-          if (event_time = result[:event_time])
-            event_time = event_time.dup.utc unless event_time.utc?
-            result[:event_time] = event_time.strftime("%Y-%m-%dT%H:%M:%S.%6NZ")
+          if (event_time = result[:eventTime])
+            event_time = event_time.getutc unless event_time.utc?
+            result[:eventTime] = event_time.strftime("%Y-%m-%dT%H:%M:%S.%6NZ")
           end
 
-          if (priority = result[:notification_priority])
+          if (priority = result[:notificationPriority])
             unless %w[min low default high max].include?(priority)
               raise ArgumentError, "AndroidNotification.priority must be 'default', 'min', 'low', 'high' or 'max'."
             end
-            result[:notification_priority] = "PRIORITY_#{priority.upcase}"
+            result[:notificationPriority] = "PRIORITY_#{priority.upcase}"
           end
 
           if (visibility = result[:visibility])
@@ -123,11 +125,11 @@ def encode_android_notification(v)
             result[:visibility] = visibility.upcase
           end
 
-          if (vibrate_timings = result[:vibrate_timings])
+          if (vibrate_timings = result[:vibrateTimings])
             vibrate_timing_strings = vibrate_timings.map do |t|
               encode_duration("AndroidNotification.vibrate_timings", t)
             end
-            result[:vibrate_timings] = vibrate_timing_strings
+            result[:vibrateTimings] = vibrate_timing_strings
           end
 
           result
@@ -140,7 +142,7 @@ def encode_android_fcm_options(v)
             raise ArgumentError, "AndroidConfig.fcm_options must be an AndroidFCMOptions"
           end
           result = {
-            analytics_label: check_analytics_label("AndroidFCMOptions.analytics_label", v.analytics_label)
+            analyticsLabel: check_analytics_label("AndroidFCMOptions.analytics_label", v.analytics_label)
           }
           remove_nil_values(result)
         end
@@ -159,14 +161,14 @@ def encode_light_settings(v)
           raise ArgumentError, "AndroidNotification.light_settings must be a LightSettings." unless v.is_a?(LightSettings)
           result = {
             color: encode_color("LightSettings.color", v.color, allow_alpha: true),
-            light_on_duration: encode_duration("LightSettings.light_on_duration", v.light_on_duration),
-            light_off_duration: encode_duration("LightSettings.light_off_duration", v.light_off_duration)
+            lightOnDuration: encode_duration("LightSettings.light_on_duration", v.light_on_duration),
+            lightOffDuration: encode_duration("LightSettings.light_off_duration", v.light_off_duration)
           }
           result = remove_nil_values(result)
-          unless result.key?(:light_on_duration)
+          unless result.key?(:lightOnDuration)
             raise ArgumentError, "LightSettings.light_on_duration is required"
           end
-          unless result.key?(:light_off_duration)
+          unless result.key?(:lightOffDuration)
             raise ArgumentError, "LightSettings.light_off_duration is required"
           end
           result
@@ -190,7 +192,7 @@ def encode_apns(apns)
           result = {
             headers: check_string_hash("APNSConfig.headers", apns.headers),
             payload: encode_apns_payload(apns.payload),
-            fcm_options: encode_apns_fcm_options(apns.fcm_options)
+            fcmOptions: encode_apns_fcm_options(apns.fcm_options)
           }
           remove_nil_values(result)
         end
@@ -213,7 +215,7 @@ def encode_apns_fcm_options(options)
           return nil unless options
           raise ArgumentError, "APNSConfig.fcm_options must be an APNSFCMOptions" unless options.is_a?(APNSFCMOptions)
           result = {
-            analytics_label: check_analytics_label("APNSFCMOptions.analytics_label", options.analytics_label),
+            analyticsLabel: check_analytics_label("APNSFCMOptions.analytics_label", options.analytics_label),
             image: check_string("APNSFCMOptions.image", options.image)
           }
           remove_nil_values(result)
@@ -331,7 +333,7 @@ def encode_fcm_options(options)
           return nil unless options
           raise ArgumentError, "Message.fcm_options must be a FCMOptions." unless options.is_a?(FCMOptions)
           result = {
-            analytics_label: check_analytics_label("Message.fcm_options", options.analytics_label)
+            analyticsLabel: check_analytics_label("Message.fcm_options", options.analytics_label)
           }
           remove_nil_values(result)
         end
diff --git a/lib/firebase/admin/messaging/send_response.rb b/lib/firebase/admin/messaging/send_response.rb
new file mode 100644
index 0000000..c0658a4
--- /dev/null
+++ b/lib/firebase/admin/messaging/send_response.rb
@@ -0,0 +1,31 @@
+module Firebase
+  module Admin
+    module Messaging
+      # The response received from an individual batched request.
+      class SendResponse
+        # A message id string that uniquely identifies the message.
+        # @return [String]
+        attr_reader :message_id
+
+        # The error if one occurred while sending the message.
+        # @return [Error]
+        attr_reader :error
+
+        # A boolean indicating if the request was successful.
+        # @return [Boolean]
+        def success?
+          !!@message_id
+        end
+
+        # Initializes the object.
+        #
+        # @param [String, nil] message_id the id of the sent message
+        # @param [Error, nil] error the error that occurred
+        def initialize(message_id:, error:)
+          @message_id = message_id
+          @error = error
+        end
+      end
+    end
+  end
+end
diff --git a/lib/firebase/admin/messaging/utils.rb b/lib/firebase/admin/messaging/utils.rb
index 7a8e832..1affd20 100644
--- a/lib/firebase/admin/messaging/utils.rb
+++ b/lib/firebase/admin/messaging/utils.rb
@@ -61,11 +61,10 @@ def check_color(label, value, allow_alpha: false, required: false)
           return nil unless value || required
           raise ArgumentError, "#{label} is required" unless value
           raise ArgumentError, "#{label} must be a string" unless value.is_a?(String)
-          unless /\A#[0-9a-fA-F]{6}\Z/.match?(value) || (/\A#[0-9a-fA-F]{8}\Z/.match?(value) && allow_alpha)
-            raise ArgumentError, "#{label} must be in the form #RRGGBB" unless allow_alpha
-            raise ArgumentError, "#{label} must be in the form #RRGGBB or #RRGGBBAA"
-          end
-          value
+          return value if /\A#[0-9a-fA-F]{6}\Z/.match?(value)
+          return value if /\A#[0-9a-fA-F]{8}\Z/.match?(value) && allow_alpha
+          raise ArgumentError, "#{label} must be in the form #RRGGBB" unless allow_alpha
+          raise ArgumentError, "#{label} must be in the form #RRGGBB or #RRGGBBAA"
         end
 
         def to_seconds_string(seconds)
diff --git a/lib/firebase/admin/version.rb b/lib/firebase/admin/version.rb
index 6295b6b..9217121 100644
--- a/lib/firebase/admin/version.rb
+++ b/lib/firebase/admin/version.rb
@@ -2,6 +2,6 @@
 
 module Firebase
   module Admin
-    VERSION = "0.2.0"
+    VERSION = "0.3.0"
   end
 end
diff --git a/spec/unit/firebase/admin/messaging/message_encoder_spec.rb b/spec/unit/firebase/admin/messaging/message_encoder_spec.rb
index c83d3bb..d70e620 100644
--- a/spec/unit/firebase/admin/messaging/message_encoder_spec.rb
+++ b/spec/unit/firebase/admin/messaging/message_encoder_spec.rb
@@ -78,24 +78,24 @@
         sound: "sound",
         tag: "tag",
         image: "image",
-        click_action: "click_action",
-        body_loc_key: "body_loc_key",
-        body_loc_args: ["body_loc_args"],
-        title_loc_key: "title_loc_key",
-        title_loc_args: ["title_loc_args"],
-        channel_id: "channel_id",
+        clickAction: "click_action",
+        bodyLocKey: "body_loc_key",
+        bodyLocArgs: ["body_loc_args"],
+        titleLocKey: "title_loc_key",
+        titleLocArgs: ["title_loc_args"],
+        channelId: "channel_id",
         ticker: "ticker",
         sticky: true,
-        event_time: current_time.dup.utc.strftime("%Y-%m-%dT%H:%M:%S.%6NZ"),
-        local_only: true,
-        notification_priority: "PRIORITY_MIN",
-        vibrate_timings: %w[0.250000000s 0.250000000s],
-        default_vibrate_timings: true,
-        default_sound: true,
-        light_settings: encoded_light_settings,
-        default_light_settings: true,
+        eventTime: current_time.dup.utc.strftime("%Y-%m-%dT%H:%M:%S.%6NZ"),
+        localOnly: true,
+        notificationPriority: "PRIORITY_MIN",
+        vibrateTimings: %w[0.250000000s 0.250000000s],
+        defaultVibrateTimings: true,
+        defaultSound: true,
+        lightSettings: encoded_light_settings,
+        defaultLightSettings: true,
         visibility: "SECRET",
-        notification_count: 5
+        notificationCount: 5
       }
     }
 
@@ -115,8 +115,8 @@
           blue: 0x22 / 255.0,
           alpha: 0xFF / 255.0
         },
-        light_on_duration: "0.100000000s",
-        light_off_duration: "0.100000000s"
+        lightOnDuration: "0.100000000s",
+        lightOffDuration: "0.100000000s"
       }
     }
 
@@ -126,7 +126,7 @@
 
     let(:encoded_android_fcm_options) {
       {
-        analytics_label: "android_analytics_label"
+        analyticsLabel: "android_analytics_label"
       }
     }
 
@@ -144,13 +144,13 @@
 
     let(:encoded_android) {
       {
-        collapse_key: "collapse_key",
+        collapseKey: "collapse_key",
         priority: "high",
         ttl: "1.500000000s",
-        restricted_package_name: "test_package_name",
+        restrictedPackageName: "test_package_name",
         data: {foo: "bar"},
         notification: encoded_android_notification,
-        fcm_options: encoded_android_fcm_options
+        fcmOptions: encoded_android_fcm_options
       }
     }
 
@@ -170,7 +170,7 @@
       {
         headers: {"apns-priority": "10"},
         payload: encoded_apns_payload,
-        fcm_options: encoded_apns_fcm_options
+        fcmOptions: encoded_apns_fcm_options
       }
     }
 
@@ -279,7 +279,7 @@
 
     let(:encoded_apns_fcm_options) {
       {
-        analytics_label: "analytics-label",
+        analyticsLabel: "analytics-label",
         image: "image"
       }
     }