How to add a second digital ID to Apple Wallet on shared Apple ID devices?

I added digital ID to my phone but am unable to add it to my wife's phone -- we use the same Apple ID for both phones...is that the problem?

I got an error that indicated it could not add a second digital ID on her phone.

Thanks.

[Re-Titled by Moderator]

Original Title: Can't add digital ID to my wife's apple wallet on her phone after adding it to mine -- we share the same Apple ID