How to create a sequence number for the ERS invoices

Hi,

The ERS invoices are being created with combination of "ERS-receipt number-sequence number" in the invoice number field. In our case, we just replace with supplier invoice number. We used to maintain the voucher number for all the AP invoices for our internal correspondence.

Since, ERS invoices generated automatically and there is no feasibility of updating the voucher number the communication and finding the correct invoice has become a bit difficult for the users. If voucher number, they can directly find by giving from and to and get the records.

Is there any other possibility in which I create a sequence number for the ERS invoices? I tried with form personalization and not allowed to get the sequences. Please share any idea on this.