uploading of GPS data does not work, if app is limited to a group

I'm using the latest version of phonetrack 0.1.1 on Nextcloud 12.0.4.

I installed the app and limited it to a group (so that only a few people can use it). Then I've noticed that the GPS Logger app on Android can't upload the data. I checked the debug log of the Android app and saw the following error: Could not send to custom URL.

I tried to send the request manually and got the following message from nextcloud:

Access forbidden
App is not enabled

There are no errors in the nextcloud.log, the web server log, and the PHP log.

As soon as I uncheck the Limit to groups box, everything works.