Hey, I can see in your pic that your Aimpoint_Front_1 socket has the Z axis pointing to the side. Rotate the socket so that the Z axis points up, while the X axis keeps pointing forward. All aimpoint sockets must have the Z axis up and the X axis forward.
It looks like there’s already a bone there at the front sight (which I guess came from Maya), but that’s not a problem, just rotate the socket inside Unreal.
Also rotate your FP_Camera socket in your character’s head, so that the Z axis points up while the X axis points forward