Somebody once repaid a debt to me via post office money order.
My bank wouldn’t take it...apparently they are too easy to counterfeit. I told them I would be glad to wait a week, or even two, for the funds to be made available, so they could be sure the money order cleared...nope.
Then I went on a strange journey, stopping by 4 post offices a couple of times each day, to see if their drawer ever had enough in it to cash the money order. The postal workers didn’t care one bit about my predicament, or their institution’s obligation to redeem the money order.
It took two and a half days to get cashed.
It was a little lesson in how much ‘full faith and credit’ our government institutions really have.
USPS has about 50,000 cashdrawers, so figure $50 a hit ~ and that's several million bucks just sitting there ~ plus there's a risk of robbery.
What you forgot was peeps got bosses ~ just ask for the supervisor next time, or ask for the postmaster. They always have a bit more money in the safe!
Same thing at the bank ~ BTW, if you had an account with the bank they'd taken the money order ~ but if you wanted cash on the spot, the banks are not post offices.