Hello Darren,
Several things can occur here.
1) Try to spray WD-40 into the push button/tumbler door for the key.
Let it soak and try to turn the key CW and CCW carefully several time.
Mostly that already does the job.
2) If that doesn't work,
roll down your passenger side window and look through the window's gap into the door where the door handle is.
Soak that area with a WD-40 can with its long nozzle as well.
3) If that also doesn't help, you need to remove the door panel (see the Wiki or do a search here) in order to gain access to the area where the door handle push rocker switch engages the inner parts of the door lock. Does that attach properly in both directions (CW and CCW), is there anything blocked?
Remove the door lock in the door (not the handle but the locking mechanism itself) with the three large Phillips screws
and see whether everything works and turns freely.
4) Sometimes you need to take the door handle of and dissassemble it.
A good cleaning and careful greasing will do the job.
Look out whether something is broken.
5) You can adjust the protruding length of the rocker switch with its internal slotted screw. Soak these parts with WD-40 properly before. Otherwise the adjustment screw might not turn.
The pics show two sedan door handles where the push rocker switches are shorter. Those can be interchanged.
Good luck,
Achim
(doorlockcollector)