Thanks for the reply!
That option was already ticked but I still don't get the messages.
I also don't see them in my contact-list.
On the facebook-website these messages go to "message requests". But in Miranda I can't see the contact or the message.
Thanks for your help!
edit:
So I checked the log and there is no incomming message. It only shows [2021-05-17 14:36:46 37CC] [Facebook_1] Received message of type=13, flags=0, body length=0 at the time I sent the message from the not friend account