Our king of account shutdowns, miles per day, is back again. This time, the cashback feature tied to the Capital One website has been restricted. Based on his guess, it may be because he shared his cashback link with a few friends to use, probably something like a buying group or reseller operation with lots of orders.
This really isn’t Capital One’s fault. In general, cashback portals will not pay resellers in situations like this if they can identify the activity.
If you really want to use cashback portals for reselling, I’d suggest opening multiple accounts and using multiple cashback portals to spread things out. That should work much better.