Can't seem to connect other gmail accounts to new Google Workspace account

Hi everyone,

I set up a Google Workspace account today to use a custom email with my squarespace site. 

I shudder to think of checking multiple gmail accounts, so I'm trying to add my other gmail accounts to the new one.

I can't get it to work - I always get a message that says "Authentication failed. Please check your username/password.

I've also tried adding the custom email to an existing gmail account. I can add other gmail accounts, but I can't add the custom email from the workspace account. 

Has anyone else had this problem? 

Yes I'm having the same problem and cannot add a new account despite it being set up in Squarespace domain.