son unable to join other sons realm despite being on it before

hi all

My son has been playing on his realm server for a while and his friends can connect no problem. My other son on another pc was able to join earlier thru an invite. He quit the game and now when he tries to get on without an invite he gets the "buy a realm?" popup. prior threads with work arounds seem to not work.

an obvious way around it is to reinvite. that works fine. But if he closes minecraft he cannot get back in. He would like access when the other son is not home and cannot invite him.

Any thoughts why this would be?

It appears the game is updated, the account in question has no realms subscription or trial. Only the other son has the realm subscription.

you can see "play" is greyed out.

thank you