why is my friend's name turning into group message under chats

Hello i was chatting with my friend on messenger and after a while his name turned into "Group messages" and couldn't be able to send him a message

I'd this on Facebook messenger? Which phone you have?I'll leave a link to register so you can communicate here, as a guest account u cant .https://forums.androidcentral.com/sh...d.php?t=409154

Welcome to Android Central! What if you start new conversation with him? Or delete that current conversation, and then send him a new message?