Missing skins and misplaced textures
Separate a website thumbnail issue from an issue inside Minecraft. They use different renderers, so similar symptoms can have different causes.
The import works, but the selector is missing
Check both packs in world settings. Leave and rejoin the world after enabling them. The selector recipe uses five pieces of paper in a cross, not five pieces in a row.
The menu works, but the player is invisible
Test the download in a new world with only this addon. Other packs that modify the player can conflict. If it works on its own, check the other packs before editing the skin files.
A duplicated face or misplaced colors
Make sure the PNG matches the geometry. As the creator, review both files in the skin editor and regenerate its thumbnail. Do not change pivots or rotations to fix a problem that only affects colors.
Report a reproducible issue
Send the skin link, Minecraft version, device and a screenshot showing whether the problem is on the website or in the game. Mention whether it also happens in a clean world. This helps distinguish file issues from preview and compatibility issues.