WordPress iOS app giving error on login

Hey all, I have setup a wordpressblog here: https://jazzmenendez.com/

Now I’m trying to access the page via the iOS wordpress app. On both the iPhone and the iPad I get the following error (loosely translated form german):

Login not possible

Expected status code in (200-299), got 403

Can I fix this somehow? A second blog I setup works just fine. Do I have to tweak access permissions on some files?

Any help is appreciated very much.