Why Use VATGroups

VATGroups allow you to explicitly provide the VAT totals that were calculated by your ERP.

By providing these values, Billit will use the VAT amounts supplied in the invoice instead of recalculating them.

Advantages of using VATGroups:

• Invoice totals remain identical between your ERP and Billit.
• Your ERP's VAT calculations are preserved.
• Rounding differences are minimized.
• Financial data remains consistent across systems.

How VATGroups Work

For every VAT percentage used on an invoice, provide a VAT group containing:

• The VAT percentage.
• The total taxable amount (VAT exclusive).
• The total VAT amount.
• The total amount including VAT.

Example:

"VatGroups": [
    {
        "VATPercentage": 20.0,
        "VentilationCode": "4",
        "TotalExcl": 11.32,
        "TotalVAT": 2.27,
        "TotalIncl": 13.59
    },
    {
        "VATPercentage": 10.0,
        "VentilationCode": "4",
        "TotalExcl": 11.32,
        "TotalVAT": 1.13,
        "TotalIncl": 12.45
    }
]

Billit will use the provided VAT group totals when calculating the invoice totals.

Recommended Approach

✅ Provide VATGroups whenever possible.

For each VAT rate used on the invoice:

1. Calculate the taxable amount in your ERP.
2. Calculate the VAT amount according to your ERP logic.
3. Calculate the VAT-inclusive amount.
4. Provide those values in the corresponding VATGroup.

This ensures the totals stored in Billit remain aligned with the totals generated by your ERP.

Order Line Best Practice

Many ERP systems store unit prices with a higher precision than what is eventually shown on the invoice.

A common ERP approach is:

Quantity = 3
UnitPriceExcl = 3.333333

Calculated TotalExcl = 9.999999
Stored TotalExcl = 10.00

Because the line total is rounded before export, small differences may be introduced when invoice totals and VAT amounts are calculated later on.

When sending invoices to Billit, it is recommended that order lines remain mathematically consistent:

TotalExcl = UnitPriceExcl × Quantity

In other words, the line total should be derived from the original unit price and quantity rather than from an already rounded ERP value.

Recommended Example

"OrderLines": [
    {
        "Quantity": 1.0,
        "UnitPriceExcl": 11.325,
        "Reference": "P001207",
        "Description": "Test Product",
        "TotalExcl": 11.325,
        "VATPercentage": 20.0,
        "VentilationCode": "4",
        "Unit": "pcs",
        "TotalIncl": 13.59,
        "ReductionPercentage": 0.0
    }
]

In this example:

11.325 × 1 = 11.325

The values remain mathematically consistent and Billit can correctly process the invoice totals.

Common ERP Behaviour

Many ERP systems calculate and store line totals as:

TotalExcl = Round(UnitPriceExcl × Quantity, 2)

For Billit, we recommend using:

TotalExcl = UnitPriceExcl × Quantity

using the original precision available in your ERP.

This helps ensure that order line totals, VAT groups and invoice totals remain aligned.

Combining VATGroups and Order Lines

The best results are achieved when:

• VATGroups are used to provide the VAT totals calculated by your ERP.
• Order lines remain mathematically consistent.
• Unit prices retain their original precision.
• TotalExcl values are based on UnitPriceExcl × Quantity.

By combining both approaches, Billit can accurately represent the invoice while keeping totals synchronized with your ERP.

Conclusion

For the most accurate integration with the Billit API:

• Use VATGroups whenever possible.
• Let VATGroups define the VAT totals calculated by your ERP.
• Keep order line values mathematically consistent.
• Ensure that TotalExcl = UnitPriceExcl × Quantity.
• Avoid sending prematurely rounded line totals when more precise values are available.

Following these recommendations minimizes rounding differences and helps keep invoice totals identical between your ERP and Billit.