Was that a $100 Walmart GC on MPX?

MPX & Pathfinder are wonky/buggy, but I've had $50 walmarts, $50 best buys and $100 REIs work.

I have no idea what drives that.

It almost seems like there is a manual / human element on the back end somewhere.

I would just make sure to only buy gc at places you know you will use them at anyways, even if not reimbursed.