When you sign up for Coinbase Prime, please use a different email address than any that are associated with existing Coinbase accounts. For example:
Do not use an email that's also used for a Coinbase.com account.
Do not use an email that's also used for any Institutional account (Exchange, Custody, Prime). If you already have a Prime account, you will need to use a different email to create a new account.
If you only have one email account, you may add “+prime” at the end of your email address as a workaround (i.e. john.smith+prime@coinbase.com). You will still be able to receive emails in your regular inbox. However, please note that this workaround only works for Gmail accounts.