The only reason I do this is because most of the staff have been trained to “top-up” various cards via paypoint so seem to feel more comfortable and confident carrying out the transaction.
I can completely understand where they are coming from though; I doubt many have heard people ask to deposit cash via paypoint (possible red flag 1), then there’s a bit of confusion as to how they do this as there’s no direct button (possible red flag 2), and then they see your bright coral card - which might be a conversation starter but also another possible red flag.
When you combine this with the fact that they’ll be liable for any losses, you can imagine why some staff who don’t directly own the stores get a bit worried and refuse (easier to say no and sorry to the customer than try to explain it to your boss).
I use my method because it seems to be what staff have been trained to do. Not sure who the responsibility belongs to as to how you should retrain the staff; Monzo? Paypoint? Or the individual stores?
Seems a bit of a difficult one to overcome.