I have windows 10 minecraft, and I can't join my friend's realm.

On the menu screen, my friend said there should be a "join realm" button to click on, but I do not have it.  I instead tried to join by accepting their invitation, but every time I try it would just say "failed to join realm, try again later".  I've tried multiple times throughout the course of multiple days and I have still been able to join their realm.