Correcting invoices - what’s the difference between the SUBSTITUTION and DIFFERENCES methods?

Consiglio

Ultimo aggiornamento il 2025-12-05.

With the DIFFERENCES method, amounts can be positive or negative—negative for returns and positive when adding items to the same invoice. In this case, the correcting invoice either subtracts or adds to the original invoice, meaning both the original and the correcting invoice remain valid.   With the SUBSTITUTION method, the correcting invoice replaces the original one, and the tax agency considers only the correcting invoice valid. 

 

Example: Final invoice should include 2 coca colas and 2 pastas

INV 2024-001                                         CORR 2024-001 (SUBSTITUTION method)

1 coca cola                                             2 coca cola                                                   1 pasta                                                    2 pasta                                                            20€ taxable amount                              40€ taxable amount                               4,2€ VAT (21%)                                      8,4€ VAT (21%)                                            24,2€ Total                                             48,2€ Total                                                   

INV 2024-002                                         CORR 2024-002 (DIFFERENCES method)                          

3 coca cola                                             -1 coca cola                   3 pasta                                                    -1 pasta                        60€ taxable amount                               20€ taxable amount * *       12,6€ VAT (21%)                                     -4,2€ VAT (21%)            72,6€ Total                                              -24,2€ Total 

Both methods are valid, and you can find examples of each in our Postman collection.

Example: Full refund   Original invoice

"full_amount": "24.20",
"items": [
            {
                "text": "T-shirt",
                "quantity": "1",
                "unit_amount": "20",
                "full_amount": "24.20",
                "system": {
                    "type": "REGULAR",
                    "category": {
                        "type": "VAT"
                    }
                }
            }
        ]

  CORRECTING invoice (SUBSTITUTION method)

"full_amount": "0",
"items": [
            {
                "text": "T-shirt",
                "quantity": "0",
                "unit_amount": "20",
                "full_amount": "0",
                "system": {
                    "type": "REGULAR",
                    "category": {
                        "type": "VAT"
                    }
                }
            }
        ]

  CORRECTING invoice (DIFFERENCES method)

"full_amount": "-24.20"
"items": [
            {
                "text": "T-shirt",
                "quantity": "-1",
                "unit_amount": "20",
                "full_amount": "-24.20",
                "system": {
                    "type": "REGULAR",
                    "category": {
                        "type": "VAT"
                    }
                }
            }
        ]