Thanks for attaching the screenshot; it's from the 50% discount pack. Where is the error you're saying you see?
Viewing post in Medieval Dungeon 48x48 Tileset (RPG Maker MV / MZ) comments
The set is 25.5
And separately (if you add them all up) it's 25.5
The price is the same whether you buy them together or separately. It is automatically calculated by the ITchio platform and I can confirm this because I just counted them all together.
Can you recalculate it? I'll wait for your reply so I can try to help you with whatever you need.