Mine’s brand new and had it a couple of times already. What I found worked was locking and unlocking a few times. listen to the “clunk” it makes when locking, I found when I heard a louder/different “clunk” the flap would open when the car was unlocked after that.
Please excuse spelling/typos. Apart from being a clot it turns out I had one on my cerebellum that's now causing various problems!