- Fixed. The missing controls now appear at:

Plans & Platform > Plans, Prices & Entitlements > Groups Available for 
each tier.
Config > Feature Availability > Groups Enabled as the global master 
switch.

api/messages.php

@@ -33,8 +33,15 @@ function messagePayload(array $row): array {
 
 function requestedGroup(array $user): ?int {
     $groupId = normalizeGroupId($_POST['group_id'] ?? $_GET['group_id'] ?? null);
-    if ($groupId !== null && !groupsEnabled()) {
-        jsonResponse(['error' => 'Private groups are currently disabled', 'groups_enabled' => false], 403);
+    if ($groupId !== null && !groupsAvailableForUser($user)) {
+        $error = groupsEnabled()
+            ? 'Private groups are not available on your tier'
+            : 'Private groups are currently disabled';
+        jsonResponse([
+            'error' => $error,
+            'groups_enabled' => false,
+            'groups_platform_enabled' => groupsEnabled(),
+        ], 403);
     }
     requireGroupAccess($user, $groupId);
     return $groupId;
@@ -174,8 +181,9 @@ function pollMessages(): never {
         'messages' => array_map('messagePayload', $rows),
         'online' => (int)$onlineStmt->fetchColumn(),
         'recording' => $recording,
-        'groups' => groupsEnabled() ? userGroups((int)$user['id']) : [],
-        'groups_enabled' => groupsEnabled(),
+        'groups' => groupsAvailableForUser($user) ? userGroups((int)$user['id']) : [],
+        'groups_enabled' => groupsAvailableForUser($user),
+        'groups_platform_enabled' => groupsEnabled(),
         'group_id' => $groupId,
         'server_time' => time(),
     ]);