Are you giving your horse time to make the right choice?
Here I give this new training horse a get ready command so she knows to pay attention and then I move slowly over a course of seconds to help her decide to move laterally. Its easy to just start tapping your horse until they move but that comes with the danger of making them dull. Just the ask or cue from a distance is enough for her to say....ok this is my choice is this what you wanted. Less is more!!