Friends can't join MCPE realm

Hi there, I've been having some trouble with my minecraft realm. I can invite my friends and they get the invitation but they can't accept it. They would just click repeatedly on the accept button but nothing would happen. I should also mention that it worked for 30 days, then after I payed my subscription it didn't work anymore.Thank you for your help in advance.
Me (realm owner) Samsung Galaxy s7 edge
My friends:
Iphone 4
Samsung galaxy s6
Iphone 6 plus
Iphone 5
Iphone 4