This is an array

settings/ajax/enableapp.php

@@ -3,7 +3,7 @@
 OC_JSON::checkAdminUser();
 OCP\JSON::callCheck();
 
-$groups = isset($_POST['groups']) ? (string)$_POST['groups'] : null;
+$groups = isset($_POST['groups']) ? (array)$_POST['groups'] : null;
 
 try {
 	OC_App::enable(OC_App::cleanAppId((string)$_POST['appid']), $groups);