Invalid contract address or token ID

When you list an item for sale from your wallet, we have to scan the smart contract and make sure it will work on our marketplace.
If you see a message that says:
"invalid smart contract" or "not a valid smart contract": you are using an address that DOESN'T belong to a smart contract. Double check your address is correct by looking it up on viewblock.
This item cannot be resold: The creator of this item doesn't want people to sell it.
Token ID doesn't exist: You entered a wrong token ID that doesn't exist on the smart contract.