I'd say you need a new key fab.
Go down and talk to Paul in service. You will be in Good hands.
Either the actuator is weak/inoperable or the actuator arm came loose. Can you lock/unlock the door from the inside using the button? Either way, door needs to be taken apart. Any reputable auto repair shop can take care of it. If you are comfortable with the dealership fixing it, good. Can't speak to the dealership, but Titus-Will Collision is really good. Don't know if they will repair your door or not.
Try taking it to Lakewood Ford or Sunset Ford that won't gouge you for the diagnostic. Good luck.
It could be bad wiring to that door if it is working for all other doors but not that door specifically, maybe an issue with the solenoid with that door?
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