Minting an item: If your transaction failed during minting an item, most likely either you are using the wrong address in your wallet and you are not the creator of the store. If you are the creator of the store and using the same address - then most likely you already minted the token you are trying to mint. If you have multiple tabs open and try to mint tokens back to back, you will run into this error. You can only mint a token once, so if you made token number 5 already - you can't make another that is also token 5.