Two domains but not able to use 2 emails

Site URL: http://www.laurajessicawalker.com

Hi

Hoping someone can help. I have had a rebrand which includes a name change. This has meant purchasing a new domain which I now have linked to the site until my 90 days is over and then I will transfer it to squarespace.
I have added my new domain to my google workspace to enable me to use the new email address but I can't add a new user to my workspace account through square space. It only gives me the option of the original domain. Can anyone help me with this?