If it has the cheap little locks are are screwed together, they can be adjusted and sometimes have to be! You can use a little graphite on your key to help lubricate the lock. You also have to may have to push the access door in a little before locking it to make sure it catches properly on the metal trip. I have struggled with (and replaced) many of the cheap locks over my 9 campers.
Becky Fisher camps in an 2022 Gulf Stream Envision SVT 21QBS.