Apply Pose as Rest pose doesn't work

Question

Just as the title says. This is the pose I want to be the new rest pose:

This is the current rest pose:

But when I try to set my pose as rest pose, the armature becomes detached from the mesh, like so:

I've looked at other questions surrounding this problem and tried to fix it, but none of them work. This includes removing armature modifier, applying pose as rest pose, then adding it back and reparenting. I've tried keeping the armature modifier and applying pose as rest pose, still doesn't work. I know there's a way to fix this, because I figured it out in the past but now I can't remember how I did it! xD

Thank you in advance.

Answer 1

If the bones stay in place when you apply the pose, and only the mesh moves, there's a simple solution:

The correct procedure, in this case, is:

Prepare the desired pose. Apply armature modifier to the mesh. Apply pose as rest pose. Select the mesh, shift select the armature, Press Ctrl P > Armature Deform.

If the bones also move when applying the pose as rest pose, it depends by the mechanism of the rig: it has to be inspected to restore its functionality in the new rest pose.