I do something like this. We can't use our Walmart credit card to buy a money order to pay the rent, without triggering the Cash Advance rate, but iBotta lets you buy Walmart gift cards at a 0.5% rebate into the iBotta account and then you can pay for a money order with up to 3 gift cards. They don't let you use a cash back credit card, but debit is fine.
The money orders are 90 cents, but the rewards for buying $850.90 worth of gift cards on iBotta are $4.25. So a net profit of $3.35 each time I pay the rent.
Technically, you could write out the money orders to yourself and cash them at your bank, but you'd probably get a suspicious teller reporting you to Treasury or something.
The opportunity came up when I was paying immigration fees for my spouse. They accept credit cards, but you never know when they'll run them, and the fee is bigger than the points. But I had to send them thousands of dollars and even at the low returns using the iBotta trick I basically managed to get like $10 back and a few free money orders.
