Manual Payment is an option that allows the purchaser to request the payment process to be taken off the GO1 system and settled in another way. This could be requesting a tax invoice or adding purchase of the course to an exisiting account they have with the portal administrator.
The customer can send a manual payment request which will trigger an email to the portal administrator or an email address nominated across the portal (in Portal settings> configuration) or per course in the course's Settings> Price and Enrollment page.