How does bill management portal number the receipts ?

Summary:

We have enabled bill management portal and we need to know how the receipt is numbered when a payment is made from customer's account from the portal. I see that is uses invoice number_today's date as a format for receipt number.

Content (required):

We have enabled bill management portal and we need to know how the receipt is numbered. I see that is uses invoice number_today's date as a format for receipt number. Is there anywhere we can control the numbering?

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