How to get permissions of an app user in an app?

I’m using Atlassian connect express. In a webhook callback I try to get the permissions of a app user, that just assigned an issue. I use:

/rest/api/3/mypermissions?permissions=ASSIGN_ISSUES

This works for all users, but other app users get a message:

"{"error": "Add-on 'Addon' disallowed to impersonate the user because 'no valid active user exists'"}"

How can I get the permissions of an app user in an app?

If I’m reading your question right, you’re app1 but are trying to impersonate app2? My guess is that it’s not going to work (I’m actually hoping that you can’t do that since somebody could impersonate another vendor which would be not so much fun… ).

/Daniel