Without looking at it, I can't tell. But sometimes the latch mechanism will get sprung in the shut position accidentally when the door is open. When that's the case you need to put a screw driver or something that you can pry with into the latch to rotate the latch back into the open position.
But without seeing it, that's just a wild ass guess.
2017 Winnebago Adventurer 37F
2016 Lincoln MKX Toad