diff --git a/public/modules/custom/asu_api/src/Api/BackendApi/Request/CreateApplicationRequest.php b/public/modules/custom/asu_api/src/Api/BackendApi/Request/CreateApplicationRequest.php
index eaebbb4b..62c05dd0 100644
--- a/public/modules/custom/asu_api/src/Api/BackendApi/Request/CreateApplicationRequest.php
+++ b/public/modules/custom/asu_api/src/Api/BackendApi/Request/CreateApplicationRequest.php
@@ -53,7 +53,7 @@ public function toArray(): array {
       'application_type' => $this->application->bundle(),
       'ssn_suffix' => $this->application->main_applicant[0]->personal_id,
       'has_children' => $this->application->getHasChildren(),
-      'additional_applicant' => $this->getApplicant(),
+      'additional_applicant' => $this->getAdditionalApplicant(),
       'right_of_residence' => NULL,
       'project_id' => $this->projectUuid,
       'apartments' => $this->getApartments(),
@@ -105,11 +105,11 @@ protected function getApartments(): array {
    * @return object
    *   Applicant information.
    */
-  protected function getApplicant(): ?object {
+  protected function getAdditionalApplicant(): ?object {
     if (!$this->application->hasAdditionalApplicant()) {
       return NULL;
     }
-    $applicant = $this->application->getApplicant()[0];
+    $applicant = $this->application->getAdditionalApplicants()[0];
     return (object) [
       'first_name' => $applicant['first_name'],
       'last_name' => $applicant['last_name'],
diff --git a/public/modules/custom/asu_api/src/Api/BackendApi/Request/SalesCreateApplicationRequest.php b/public/modules/custom/asu_api/src/Api/BackendApi/Request/SalesCreateApplicationRequest.php
index f225228b..9b81552e 100644
--- a/public/modules/custom/asu_api/src/Api/BackendApi/Request/SalesCreateApplicationRequest.php
+++ b/public/modules/custom/asu_api/src/Api/BackendApi/Request/SalesCreateApplicationRequest.php
@@ -61,7 +61,7 @@ public function toArray(): array {
       'application_type' => $this->application->bundle(),
       'ssn_suffix' => $this->application->main_applicant[0]->personal_id,
       'has_children' => $this->application->getHasChildren(),
-      'additional_applicant' => $this->getApplicant(),
+      'additional_applicant' => $this->getAdditionalApplicant(),
       'right_of_residence' => NULL,
       'is_new_permit_number' => NULL,
       'project_id' => $this->projectUuid,
@@ -115,11 +115,11 @@ private function getApartments() {
    * @return array
    *   Applicant information.
    */
-  private function getApplicant() {
+  private function getAdditionalApplicant() {
     if (!$this->application->hasAdditionalApplicant()) {
       return NULL;
     }
-    $applicant = $this->application->getApplicants()[0];
+    $applicant = $this->application->getAdditionalApplicants()[0];
     return [
       'first_name' => $applicant['first_name'],
       'last_name' => $applicant['last_name'],
diff --git a/public/modules/custom/asu_application/src/Entity/Application.php b/public/modules/custom/asu_application/src/Entity/Application.php
index 5ed6d70b..9ea8dde4 100644
--- a/public/modules/custom/asu_application/src/Entity/Application.php
+++ b/public/modules/custom/asu_application/src/Entity/Application.php
@@ -144,7 +144,7 @@ public function getMainApplicant(): ?array {
    * @return array
    *   Array of applicants.
    */
-  public function getApplicant(): array {
+  public function getAdditionalApplicants(): array {
     return $this->applicant->getValue() ?? [];
   }
 
diff --git a/public/modules/custom/asu_application/src/Form/ApplicationForm.php b/public/modules/custom/asu_application/src/Form/ApplicationForm.php
index 52d94395..6994c08b 100644
--- a/public/modules/custom/asu_application/src/Form/ApplicationForm.php
+++ b/public/modules/custom/asu_application/src/Form/ApplicationForm.php
@@ -200,6 +200,26 @@ public function validateForm(array &$form, FormStateInterface $form_state) {
       }
     }
 
+    $has_additional_applicant = (!empty($formValues['applicant'][0]['has_additional_applicant'])) ? (bool) $formValues['applicant'][0]['has_additional_applicant'] : FALSE;
+
+    if ($has_additional_applicant) {
+      foreach ($formValues['applicant'][0] as $applicant_field => $applicant_value) {
+        if ($applicant_field == 'has_additional_applicant') {
+          continue;
+        }
+
+        if ($applicant_field == 'personal_id' && strlen($applicant_value) != 4) {
+          $fieldTitle = (string) $form["applicant"]['widget'][0][$applicant_field]['#title'];
+          $form_state->setErrorByName($field, t('Check @field', ['@field' => $fieldTitle]));
+        }
+
+        if (empty($applicant_value) || $applicant_value == '-' || strlen($applicant_value) < 2) {
+          $fieldTitle = (string) $form["applicant"]['widget'][0][$applicant_field]['#title'];
+          $form_state->setErrorByName($applicant_field, t('Field @field cannot be empty', ['@field' => $fieldTitle]));
+        }
+      }
+    }
+
     $triggerName = $form_state->getTriggeringElement()['#name'];
     if ($triggerName == 'submit-application') {
       parent::validateForm($form, $form_state);