Adding shared user

I have sucessfully installed my ring alarm and it has been running for a few weks now.I want to add my son to the app so he can arm and disarm the system if i am not home.I have gone through the steps to add him, sent him the invite, he has his own copy of the app on his phone, he has responded to my email invite but when he clicks the link to respond all he has is a blank white page with nothing on it. I get no notification that he has accepted or declined the invite. Therefore he cannot be linked to the main account to control the arm/disarm of the alarm system.Does anyone have any idea of what is going on, i have triple checked ALL settings and they are all as they should be, the invite was sent, then re-sent with the same result for my son of a blank white page when he tries to accept.Any and all advice appreciated as this is doing myhead in !