I do have EliMZ_Book and EliMZ_SkillCost for my RPG Maker MZ project.
But uh-update on testing:
I considered the possibility that I should use a more up-to-date version of MZ so I loaded the project on my Steam copy and it works??
Why everything EXCEPT the HPCost tag works is beyond me, though.
As for pressing F8/12, itch is not letting me respond with the picture, so I hyperlinked it instead.
I believe itch io does not accept copy and paste. You should save a png file and then upload it to the itch io post.
By the screenshot, the error seems that the value passed into the meta tag HpCost is not a string. But I can't seem to find a reason for that. I believe I will need a sample project from you replicating the error so I can take a look and see what the problem is. I tested it here and it worked just fine.
