So, I did a skin for the XRR car on paint.net and saved it, but when I hop in LFS this error pops up saying that it's "impossible" to load my skin
what do I do to fix this?
any help appreciated

It doesn't matter where you made skin. Just make sure to name it XRR_somename and place it in skins folder. The file type should be jpg and image resolution 1024×1024px. If you want other players to see your skin, then you additionaly have to upload it to lfs world.

Quote from rane_nbg :

It doesn't matter where you made skin. Just make sure to name it XRR_somename...

How do i upload my skin, im in a online server but then pops a message saying
Your skin was not found in lfs/skin any help?

Login to your lfsworld.net then navigate to skins icon, then upload your skin in 1024x1024px resolution and jpg format.

Quote from iitz0ctane :

How do i upload my skin, im in a online server but then pops a message saying ...

https://www.lfs.net/account/skins

you need skin slots, demo users don't get any by default, but you can buy them with LFS credit.

each license tier also grants you 25 skin slots