1. lift the washer 45 degrees back , then secure it with something.
2 try to move (rotate) the coupler with your fingers.
if does not moves freely , means that you did not install the coupler as should be.
remember, in one direction the agitator will moves.
in the other direction its for spin (drum rotates)
If this coupler rotates freely might be motor connector, specially check the red cable.
i hope helps.