There are a couple of reasons which will deposit tokens to your contract balances:
- You have bought a USD sale and there was a small difference between the submitted price and the price on the blockchain.
- You have bid on an auction and were outbid. We can't refund the amount automatically as it is a potential attack vector.
- You have created a collection and set the collection fee > 0% and someone bought one of your NFTs on the secondary market.