Invoice and receipt number

Dear all,

I’m having some issues with the receipt and the invoice numbers.

The invoice number is added to the the receipt number but not the reverse.

An example:
Starting from number,
First order with receipt, the receipt will be number 1;
Second order with invoice, the invoice will be number 2;
Third order with receipt, the receipt will be number 2;
Fourth order with invoice, the invoice will be number 4.

How can I separate the invoice and receipt numbers?

Thanks a lot,
Federica

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