Are you sure that you inserted the cable when the shifter was in the correct position.

It will go in when the shifter is at either end of the click / gear range, but only one is correct, and will allow it to shift.

If you shine a light into the shifter hole, you will be able to see where the end of the cable sits when the position is correct. insert it fully, then hold the cable tight, use the shifter, and you will feel it pull the cable in.