ERPNext Customization — 2

I need this customization on ERPNext
The approach is as below
We will have one default supplier for this case supplier named
Government (Duties)

Thirdparty Payments
So we create a specific series for purchase invoice i.e
DN-#####
i.e DN-00001 hence forth
Records for creation of this purchase invoice are pulled from an already developed API. Whick lists all the items and charges
Then we also capture payment entries for this invoice from specific cheques as pulled from the API. Fields will be Invoice Number and Amount.
There is a unique Serialization on the records i.e. Ref No to eliminate duplication. Also Client ID can be captured as a Custom Field on the respective Purchase Invoice.

Client Refunds
We link the above created Purchase Invoice and Create a Sales Invoice with a series
REQ-#####
i.e. REQ-00001 henceforth
We link the purchase invoice and fetch all the items with same amounts.
We can use the Client ID to Identify the Specific Client and the Ref No. These can be obtained from the API/Purchase Invoice already created above.
So when payment entries are done against this Invoice for full amount. The balance and specific accounts to balance to 0 for the Clients Ledger.

Please note, this should not capture as income at any point of the chart of accounts.

Also on Accounts after Accounts Payable
We will have a Sub Section as Below

Third Party Duty Payments & Refunds
Thirdparty Payments (To Open Purchase Invoices with Series DN-##### by applying filters)
Client Refunds (To Open Sales Invoices with Series REQ-##### by applying filters)

Then on main Purchase invoice and Sales Invoice we just add a filter not to show series for the above both on Purchase and Sales. This to avoid confusion.