From an invoice saved search, how do you get the primary contact info? I am doing contact (primary) fields, but it is not reflecting what is in the customer relationship primary contact

IIRC, you go to the customer record, since that's where the contact is. Select the "Customer Fields..." linked record and then select the "Primary Contact" field there. If you need more of the contact's details than just the name, you'll need to run a customer record saved search, or choose a different reporting method.

Yeah, I need more than just the name. I need an email

yep, then start with a customer search and reach back out to the transaction records from there