You can invite a joint account holder under your Profile page.
You will need to provide the following joint account holder's information for the invitation:
Legal First Name
Legal Last Name
SSN Last Four Digits
Email
It is important that they use identical information when accepting and applying for the Reservoir.
If your joint account holder is receiving the "Invite Not Valid" message it may be because there is an information mismatch between the application and invitation. Resend the invite to them using the information from their application.