Fence needs replacing, supported by retaining wall. Who pays for retaining wall that needs repair?

Our property is on the high side, and the wall sits under the fence going on to our back neighbour. we need to repair the retaining wall or the new fence is just going to fall down.

https://preview.redd.it/an2k4r6yq7cg1.jpg?width=5712&format=pjpg&auto=webp&s=773a9aa0c1ead549bf9d0df7301d2653061d5cc1