Hello Fabian,
can you please provide a sample of the URL you are trying to connect with along with the log message shown when connecting?
Please note that the base URL of the Mantis installation is required here (No /login_page.php etc.).
Also you should make sure that the REST API is enabled in your Mantis installation:
should contain
1 | $g_webservice_rest_enabled = ON; |
Hope this helps,
Torsten