iOS mail app no longer connects after changing to login 2.0

I logged in to the mailbox.org website. Changed to login 2.0. I did not change my username and password.

Result: my iOS mail app gave an error, could no longer connect to mailbox.org.

I deleted the account in iOS, and added it again following these instructions:

https://kb.mailbox.org/en/private/e-mail/setting-up-mailbox-in-the-ios-mail-app/

Unfortunately, no success. The iOS app does not connect to mailbox.org (actually: nothing happens).

Then set up an e-mail app password, and tried that. No luck, iOS says wrong username/password.

What am I missing? Is there a updated manual somewhere? I've used mailbox.org for years without any problems. Now I can no longer check my email using a local mail client.