This might help:https://community.shopify.com/c/authentication-and-access/multipass-identifier/m-p/2690617/highlight/true#M2717

On my road to multipass for fun and profit - I realized that you don't set the email to update the users multipass identifier or it dies.I too had the same "NULL" problem  so I went through and just created a new multipass for those null users and st...

We have a shopify plus store in the EU that we are servicing multiple marketplaces for.  We have made sure that the "read_markets / write_markets" scopes are enabled for this key we are using. We are getting a consistent access denied, and I'm using ...