I have done everything that is required and the skin is not showing.
I added admin permission - o.grant group admin customrock.use
Added admin usage - o.grant group admin customrock.spawnwith
I entered the chat command /rskin 883572447

Nothing works.
Is there something wrong with my config?
Looks like all the other ones.

{
"DefaultRockSkin": 883572447
}

Got it going.