We cannot accept extra payments made to invoices that have received a transaction in the past. You must always generate a new BitPay invoice for each payment.
This allows our system to calculate how much gas it will cost to pay the invoice. The gas fee is based on the most recent block on the Ethereum blockchain.
BitPay invoices also generate exchange rates at the time of the invoice. Accepting only one payment per invoice safeguards against cryptocurrency price volatility. You can learn more about how we get our exchange rates.
When you try to send an ETH payment to a previous invoice’s address, you will get a notification that the transaction failed. Additionally, you will lose the gas for the transaction. The value of the transaction, however, is returned to your Ethereum account.
Here’s an example of what a duplicate, failed transaction looks like on ETH blockchain explorer:
For more information on making payments to merchants using BitPay, check out our guide to paying a BitPay invoice.