Paste flipped pose doesn't work correctly.

Hello, I’m following this tutorial:

And I’m at the part where I’m supposed to paste the pose from frame 1 into frame 21 via the Paste flipped pose option.
But this doesn’t seem to work correctly for me, All it does is that it rotates to lower right leg out a bit and raises the right arm about 5°

I’ll give any additional information upon request as I don’t know what else might be useful at the moment.

is your character away from the centre of the object, or the root bone?

if it is blender will get confused because it will try to paste the flipped pose but it can’t

Also make sure L/R naming conventions are correct and check that the corresponding L/R bones have the correct roll value (usually selecting all bones and Ctrl-N will solve it) …