Auto Increment Bill Number

Need to have the Bill Number auto increment like the Invoice Number.

That's not possible Van https://akaunting.com/docs/faq/auto-bill-number

Ah, thank you. I understand now. Typically an accouting program assignes a Purchase Order (PO) number and provides it to the vendor when making an order. I assumed that the Bill Number was this puposes. Am I to understand there is no PO number then?