1.
barking up the wrong tree; misdirected; wrong address
Directing a complaint, request, or action at the wrong person or place. Originally meant going to the wrong gate (門) of a house, and now describes any situation where someone's efforts or blame are aimed at the wrong target.
Literally 'wrong gate' — from the idea of going to the wrong house by mistake. The 門 (gate) here refers to the entrance of a house in traditional Japanese neighborhoods. The お prefix adds a slight softening.
Usage
Most commonly used in the pattern お門違いだ to tell someone their complaint or request is directed at the wrong person. Can also be used attributively: お門違いの苦情 (a misdirected complaint).