diff --git a/main/auth/courses.php b/main/auth/courses.php
index 4775c2fc05..c8938f241d 100755
--- a/main/auth/courses.php
+++ b/main/auth/courses.php
@@ -173,11 +173,10 @@ if (isset($_POST['unsubscribe'])) {
 switch ($action) {
     case 'subscribe_user_with_password':
         $courses_controller->subscribe_user(
-            $_POST['subscribe_user_with_password'],
-            $_POST['search_term'],
-            $_POST['category_code']
+            isset($_POST['subscribe_user_with_password']) ? $_POST['subscribe_user_with_password'] : '',
+            isset($_POST['search_term']) ? $_POST['search_term'] : '',
+            isset($_POST['category_code']) ? $_POST['category_code'] : ''
         );
-        exit;
         break;
     case 'createcoursecategory':
         $courses_controller->categories_list($action);
diff --git a/main/inc/lib/auth.lib.php b/main/inc/lib/auth.lib.php
index db34036c41..fc9d6bd33b 100755
--- a/main/inc/lib/auth.lib.php
+++ b/main/inc/lib/auth.lib.php
@@ -605,7 +605,13 @@ class Auth
         $user_id = api_get_user_id();
         $all_course_information = CourseManager::get_course_information($course_code);
 
-        if ($all_course_information['registration_code'] == '' || $_POST['course_registration_code'] == $all_course_information['registration_code']) {
+        if (
+            $all_course_information['registration_code'] == '' ||
+            (
+                isset($_POST['course_registration_code']) &&
+                $_POST['course_registration_code'] == $all_course_information['registration_code']
+            )
+        ) {
             if (api_is_platform_admin()) {
                 $status_user_in_new_course = COURSEMANAGER;
             } else {
@@ -636,7 +642,7 @@ class Auth
             $form->addElement('hidden', 'sec_token', $_SESSION['sec_token']);
             $form->addElement('hidden', 'subscribe_user_with_password', $all_course_information['code']);
             $form->addElement('text', 'course_registration_code');
-            $form->addButton(get_lang('SubmitRegistrationCode'));
+            $form->addButton('submit', get_lang('SubmitRegistrationCode'));
             $content = $form->returnForm();
 
             return array('message' => $message, 'content' => $content);
diff --git a/main/inc/lib/course_category.lib.php b/main/inc/lib/course_category.lib.php
index 10fa9be6b2..345eb8fcf6 100755
--- a/main/inc/lib/course_category.lib.php
+++ b/main/inc/lib/course_category.lib.php
@@ -1041,6 +1041,10 @@ function getCourseCategoryUrl(
     $action = isset($action) ? Security::remove_XSS($action) : $requestAction;
     $searchTerm = isset($_REQUEST['search_term']) ? Security::remove_XSS($_REQUEST['search_term']) : null;
 
+    if ($action === 'subscribe_user_with_password') {
+        $action = 'subscribe';
+    }
+
     $categoryCodeRequest = isset($_REQUEST['category_code']) ? Security::remove_XSS($_REQUEST['category_code']) : null;
     $categoryCode = isset($categoryCode) ? Security::remove_XSS($categoryCode) : $categoryCodeRequest;