diff --git a/.github/ISSUE_TEMPLATE/bug_report.yml b/.github/ISSUE_TEMPLATE/bug_report.yml
index 04be6e7..c0779d7 100644
--- a/.github/ISSUE_TEMPLATE/bug_report.yml
+++ b/.github/ISSUE_TEMPLATE/bug_report.yml
@@ -74,6 +74,7 @@ body:
         - Python 3.9
         - Python 3.8
         - Python 3.7
+        - Python 3.6
       default: 1
     validations:
       required: true
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index c0d8d00..d67b8ee 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -16,7 +16,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-20.04, windows-2022, macOS-13]
-        python-version: [3.7, 3.8, 3.9, 3.10.0, 3.11.0, 3.12.0]
+        python-version: [3.6, 3.7, 3.8, 3.9, 3.10.0, 3.11.0, 3.12.0]
     steps:
       - uses: actions/checkout@v2
       - name: Set up Python ${{ matrix.python-version }}
diff --git a/dev-requirements.txt b/dev-requirements.txt
index 2028f84..03bce60 100644
--- a/dev-requirements.txt
+++ b/dev-requirements.txt
@@ -1,7 +1,7 @@
 requests==2.31.0
-setuptools==69.5.1
-wheel==0.43.0
-twine==5.0.0
+setuptools==40.8.0
+wheel==0.35.0
+twine==3.5.0
 vulture>=1.0
 bandit>=1.5.1
 pydocstyle>=3.0.0
diff --git a/requirements.txt b/requirements.txt
index 44f27bd..d8fcee2 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,4 +1,4 @@
 requests>=1.0.0
 setuptools>=40.8.0
-wheel>=0.40.0
-twine>=4.0.0
+wheel>=0.35.0
+twine>=3.5.0
diff --git a/reserver/reserver_func.py b/reserver/reserver_func.py
index 2c9d656..bbfcdc6 100644
--- a/reserver/reserver_func.py
+++ b/reserver/reserver_func.py
@@ -1,6 +1,7 @@
 # -*- coding: utf-8 -*-
 """Reserver functions."""
-from requests import get
+import requests
+import requests.adapters 
 from .reserver_param import PYPI_TEST_URL, PYPI_MAIN_URL
 from hashlib import sha256
 from time import time
@@ -32,7 +33,18 @@ def does_package_exist(suggested_name, test_pypi):
         url = PYPI_TEST_URL + "/" + suggested_name + "/"
     else:
         url = PYPI_MAIN_URL + "/" + suggested_name + "/"
-    response = get(url, timeout=5)
+
+    s = requests.Session()
+    retries = requests.adapters.Retry(
+        total=5,
+        backoff_factor=0.1,
+        status_forcelist=[ 500, 502, 503, 504 ]
+        )
+
+    s.mount('http://', requests.adapters.HTTPAdapter(max_retries=retries))
+    s.mount('https://', requests.adapters.HTTPAdapter(max_retries=retries))
+
+    response = s.get(url, timeout=5)
     return not response.status_code == 404
 
 
diff --git a/reserver/reserver_obj.py b/reserver/reserver_obj.py
index d23a065..fa771cc 100644
--- a/reserver/reserver_obj.py
+++ b/reserver/reserver_obj.py
@@ -1,6 +1,7 @@
 # -*- coding: utf-8 -*-
 """Reserver modules."""
 from .reserver_func import does_package_exist, generate_template_setup_py
+from .util import has_named_parameter
 from os import environ, path, getcwd, remove
 from shutil import rmtree
 from sys import executable
@@ -93,10 +94,13 @@ def upload(self, package_name):
         error = None
         for command in commands:
             try:
-                check_output(command, shell=True, text=True)
+                if has_named_parameter(check_output, "text"):
+                    check_output(command, shell=True, text=True)
+                else:
+                    check_output(command, shell=True)
             except CalledProcessError as e:
                 publish_failed = True
-                error = e.output
+                error = e.__str__()
                 if command == commands[-2]:
                     if "403" in error and "Invalid or non-existent authentication information" in error:
                         error = "Invalid or non-existent authentication information(PyPI API Key)."
diff --git a/reserver/util.py b/reserver/util.py
new file mode 100644
index 0000000..a02da86
--- /dev/null
+++ b/reserver/util.py
@@ -0,0 +1,19 @@
+# -*- coding: utf-8 -*-
+"""utility module."""
+from inspect import signature
+
+
+def has_named_parameter(func, param_name):
+    """
+    Check whether the given function has a parameter named param_name or not.
+
+    :param func: function to check it's params
+    :type func: function
+    :param param_name: parameter's name
+    :type param_name: str
+
+    :return: boolean
+    """
+    _signature = signature(func)
+    parameter_names = [p.name for p in _signature.parameters.values()]
+    return param_name in parameter_names
diff --git a/setup.py b/setup.py
index 5daf019..88739fa 100644
--- a/setup.py
+++ b/setup.py
@@ -49,6 +49,7 @@ def read_description():
         'Natural Language :: English',
         'License :: OSI Approved :: MIT License',
         'Operating System :: OS Independent',
+        'Programming Language :: Python :: 3.6',
         'Programming Language :: Python :: 3.7',
         'Programming Language :: Python :: 3.8',
         'Programming Language :: Python :: 3.9',