Either you do as being pointed out in the comment above, adding shaders prior (poiyomi in this case, manuka (vanilla) does not use liltoon or any other shader) to adding the avatar package, or you delete the package (which is not always resolving the issue, as some files may be left somewhere else in the project), and redo the process, or you go the simple step: Add the shader afterwards, check every clothing, hair and whatnot for the actual shader use.
If it says "internal error", click that part, go to poiyomi, progress to the latest version, click either the regular or pro version, and see the change happening (pink getting changed to bright blue and that changing to the actual texture after calculations being done).

Same goes for Jumpy (which has been found quite a long ago and quite a lot), also 300 bucks for an avi.
https://yoyogi-mori.booth.pm/items/3246471
People designing such things and setting these prices losing touch with reality.

Please use a different web hoster. Imgur, for example, not discord.

just registered to say this: thank you very much @toraa !!!