An invitation code is a personal code shared from an existing Fleek user to a newbie. It's also known as "Referral Code".
This code is used when signing up for a new account. It gives the new joinee a certain amount of free credits to try Fleek's awesome service for the first time.
Once the code is used for that first ride, the person who sent the code will also receive free credits. Invitation (referral) credits are valid for up to 7 days.