I have plenty of CRETA but it says insufficient gas

Network fees are paid in POL, never in CRETA. A wallet holding only CRETA cannot send a single transaction — not a bid, not a claim, not even reclaiming its own money.

Keep a small amount of POL in the same wallet and account you are using here. It is worth topping it up before an auction ends rather than during it.

Also check the wallet is on Polygon. POL on a different network cannot pay for anything on this one.