It sounds like this app is trying to post to the authorization endpoint, but it should be posting to the token endpoint instead?

I uploaded a new version that fixes this problem. Can you try it?

(Originally published at: https://p83.nl/p/599)

Where did you publish the .apk?

I had found this problem as well. It was fixed in f9a13363c6219e480a2ee482788cc439c46998cd

(Originally published at: https://p83.nl/p/600)

If this app is a Micropub client, it should be doing the authorization flow rather than the authentication flow.

https://indieauth.spec.indieweb.org/#authorization

In this flow, the client only makes a POST request to the token endpoint, not to the authorization endpoint.

This issue does not occur in Wrimini 0.0.10-alpha.