Digital Key

I just got a new BMW and it has a digital key. I am able to connect my iPhone to the digital key for the car as the main user. I am then allowed to invite other users. When I send an invite from my Apple Wallet to my husband I get a message-

### Cannot receive car key invitations at this time

I have gone to BMW support. I called Apple support, they told me to make sure he had the latest update on his phone (he does). I am able to invite my son and his iPhone works. No ne can tell me why my husband's phone can't connect. There must be a setting or something but I can get no answer. The point is not that we need him to use his phone as a digital key- but now that I can't figure out why it isn't working- it is bugging me VERY MUCH!!!! Please someone help me figure out why it won't work.