The reasons that I have heard for that shop being invalid are mostly due to photos.
- not photographing the water cup if you got one.
- not photographing the side items if you got one.
- not photographing the drink. I think you need to remove the lid?
Also, did you spend enough time in the store?
Did you need to go during a certain time frame?
Did you start another shop, any shop, less than 6 minutes later? I had a drive thru and a gas station in the same lot. I had both invalidated due to this unknown "rule" of theirs.
I had one invalidated in 2013 (which I just noticed) for not turning in a CPI. I also noticed that with a drink, I spent $8.