Unless I have two, I would cancel the first transaction for nonpayment before offering the second chance. This avoids a late payment and an obligation to satisfy two buyers. EBay imposes a waiting period before the seller can initiate the non-bidding payer option.

Canceling the transaction using the non-paying bidder option also assures that any listing fees are credited back to the account AND it assures that the final sales fees are retracted - otherwise, as soon as the listing is shown as "sold" (not "paid"), eBay assess the final value fee for the sales price plus the domestic shipping rate.