SQL 2016 grant local SQL user access to view

I have a SQL 2016 server which is in domain B and I need to access it from domain A. There's no domain trust between the two so if I understand this correctly AD authentication goes out the window even with a user in domain B as the cert won't match but please correct me if I'm wrong.

To get around this, I created a local SQL user (SQL authentication is set to both Windows and SQL) and now need to give this user Select permissions to a view that I've created but I keep getting this error

Msg 15151, Level 16, State 1, Line 3 Cannot find the user 'my.user', because it does not exist or you do not have permission. 

The statement I'm using to grant permissions

 USE MYDB; GRANT SELECT ON dbo.My_view_a TO "my.user";