What is potential first bid bonus?

The potential first bid bonus applies when the owner of the ordinals decides to end the auction within 144 blocks of its start. In this case, the owner must pay an additional fee to the first bidder, which is the maximum of either 5% of the debt or 0.001 BTC.

This bonus is designed to reward the first bidders for the risks they take if the price of the ordinals drops significantly during the auction. It provides an incentive for the owners to retain their ordinals, even after the auction has begun because it's easy to buy your Bitcoin Ethereum back, but it's not easy to change or buy your unique NFT back.