Brother can't send be books Docs.

For years my brother has sent me a book here and there with calebre. It always worked great until now.

He is my kindle allowed list to get files.

He can send a book to himself now problem and when he sends one to me it looks to go through but I don't get it.

I can send books to him or myself without a problem. We checked screenshots of all are settings and everything looks perfect but no joy.

No idea what to try next.