UV maps contain 2 verification pixels in the top-left corner. (If your image does not contain such pixels, download the UV map again).
Do not edit or modify those pixels, in order for the skin to be accepted.
Hello Max, i have a quick question, could you change the setting where skins get deactivated from the store if not enough people buy them in a certain time period? I literally make skins the first day and they get deactivated after a single person buys that skin that day.