Problem RCS messages

Hello and good day,

I have a problem with sending RCS messages. I regularly send messages to a friend. Sometimes the sending is canceled with the error message MMS to use. I can't see any pattern as to why it sometimes works and sometimes not. It's very annoying and irritating.

My iPhone has 18.1 installed, my provider is Deutsche Telekom and the recipient is an O2 customer.

Greetings from Germany

Rainer :)