Pay with USDC on Base — connect MetaMask or Coinbase Wallet. Near-zero fees, no account. You pay SoapBox, the seller, on Base. You'll need a little ETH on Base for gas.
Paying without a browser wallet? Send the exact amount on Base, then paste your transaction hash:
The last digits identify your payment, so send every digit: a different amount can't be matched to your order. Sending from an exchange? Make sure its fee isn't taken out of this amount.