I saw this while surfing around the Marriott webpage... I realize that this is no longer an option but what was it... I never heard of PAYBACK points...
Marriott Rewards program change: Last chance to earn PAYBACK points.
Effective June 1, 2011, members will no longer have the option to earn PAYBACK points. The last day to earn PAYBACK points or convert your Marriott Rewards points to PAYBACK points is May 31, 2011.
If you’ve currently opted to earn PAYBACK points, switching your preference is fast and easy. Visit MarriottRewards.com/myaccount, where you can update your account to earn Marriott Rewards points or miles with more than 30 airline programs.
I attached a link that refers to these payback points that was specific to Germany, back in the day for Marriott Rewards. Read down a bit and you'll see explanation.