It’s like trying to pay by contactless in the US, where you have to tell them ‘yes, your machine takes it, you have to let me tap. No, I won’t just hand you my card, I’m using my phone and that’s that, or I’m not buying anything’. Even then, some shops would rather lose a sale than allow someone to pay contactless.
Same type of thing… many shop staff are extremely afraid of change or anything that looks at all unfamiliar to them, including many managers. I know one Subway in the US where the franchise owner hid the PIN pads behind the counter (took them off the mounts) to prevent people paying by contactless. Was outright told by staff the reason was the franchise owner found out about it and wanted to make sure people couldn’t use it.
The moral of the story? Without widespread use, no matter what technologies shops support in theory, actual use can be very, very different due to staff actively preventing you from buying things/services/etc. Do not expect this to ever get better with regards to PayPoint. Cynical? Perhaps. But I just can’t fathom the types of shops that have PayPoint machines ever being totally on board with depositing cash for people.