Reading Buses have recently added contactless payment on bus. Tried twice yesterday and both attempts failed, but normal debit card worked.
I assume this is because it is an offline transaction as seen on other threads, but no specific mention of Reading Buses
The bugs thread is a little out dated and we’re working on getting that fixed. I would assume that is the problem, have you tried chip and PIN with Monzo with them?
The payment is on the bus so you just tap a reader with your card, there is no provision for chip and pin or chip and dip…imagine London Underground without contactless but inserting your card at the barrier and entering your pin, everything would grind to a halt 
Ah okay, my bad then!