To clarify, there are two different types of receipts in QBO: 1) a sales receipt and 2) a payment receipt. For me, the payment method field works as intended on sales receipts:

However, it doesn't work as intended on payment receipts. It should populate on a payment receipt as well. I personally don't find it a big deal because payment receipts are not generally issued to customers and, if they are, it still shows the balance and payment amount.