If you are in the US, is it possible to pay the driver on delivery with cash or personal check? I've made a UPS account and entered payment details, but I see no way to assign the shipping invoice to my account for online payment.
Delivery drivers in the US won't take cash. And I am sure they won't take personal checks either. I have been shipping since the 1980s. C.O.D. used to be a popular option but went away a long time ago. Driver's didn't want the responsibility and the risks.
You should find your local UPS office and try to pay there. Might be able to pay at a UPS store.
I contacted UPS. There is a phone number you can call to make payment over the phone, or you can just pay the driver with personal check on delivery. No cash as you stated, but checks are fine.