update: fix default app_url with subscribe_url

app/Http/Controllers/User/UserController.php

@@ -118,9 +118,9 @@ class UserController extends Controller
                 abort(500, __('Subscription plan does not exist'));
             }
         }
-        $subscribeUrl = config('v2board.app_url', env('APP_URL'));
+        $subscribeUrl = config('v2board.app_url');
         $subscribeUrls = explode(',', config('v2board.subscribe_url'));
-        if ($subscribeUrls) {
+        if ($subscribeUrls && $subscribeUrls[0]) {
             $subscribeUrl = $subscribeUrls[rand(0, count($subscribeUrls) - 1)];
         }
         $user['subscribe_url'] = "{$subscribeUrl}/api/v1/client/subscribe?token={$user['token']}";