Multiplayer Issue between iPad and iPhone

[betsyroper]

I have been unable to set up multiplayer between my iPad and iPhone so I can race my son in Asphalt 8. Both devices have OS 8.1.3 and are running game version 1.7.2. He is signed into game center on one device and I am signed into the other under different accounts. When we try to race each other we enter "join room" and just never see each other. We're each signed in under different Apple IDs, and different Game Center Profiles. The "Allow Invites" option is enabled on both devices. When we try to race each other, we go to the multiplayer "room" within the game, but never see each other among the racers nor have the opportunity to vote for a common route.
If I should be posting in the 3rd party app forum I apologize, but this seems to me to be an OS issue, so I thought I'd start here.

Thanks,
one frustrated momma