Did a similar thing with Agoda once. Booked flights from Bangkok-Mandalay-Bagan-Mandalay-Chiang Mai. A (too) cursory check on the internet said you can get a Visa on Arrival for Myanmar.
Got to Bangkok only to be told you needed to get a Visa first so you could use it on arrival and it was just a poorly worded government website. I would have understood if I'd paid more attention.
Bangkok Airways were brilliant and effectively converted the economy flights to two business class flights to Vientiane which was around the same price, so we went there instead.
But the hotel in Bagan would not back down on the non-ref bit, even though I said we would be back in a few months for a longer stay, so I told them to go and do one and left them several horrible reviews.