Any shops that have been made during 1.6 of EpicShop will have a bug where item's that aren't bought from a shop can't be sold to the shop.

This is fixed in this update, but you have to do a couple of things once you have downloaded (Listed Below)

Step 1: Stop the server.
Step 2: Upload the new plugin version (1.6.3)
Step 3: Back up all configs and folders in /plugins/EpicShop/
Step 4: Start the server.
Step 5: type /epicshop patch

This will patch all items in your shops, the issue was to do with NBT data being attached to items that are purchased so normal items (like stone that has been mined etc.) couldn't be sold.

Thank you to Jung in the JPS Discord for bringing this bug to my attention