I invite my friend to my world and they said they didn't receive an invite notification but I can go into their world like no problem, but can't be invited to my world.

So, I was playing my world and I want my friend in my world,so I invite him, after that he didn't go in, he said the notification doesn't go in, even if I try another network, countless time re-login and still can't invite him but when I go to his world, everything is fine with no problems.