Validation errors when creating invoices

Validation errors occur when an invoice or credit note violates the requirements of the invoicing standards (EN 16931, XRechnung, ZUGFeRD) or when required fields are not filled in correctly. This guide helps you understand and fix the most common errors.

Required fields are empty or missing

The most common cause of validation errors is missing required fields.

Which fields are required?

When creating an invoice, the following fields must always be filled in:

• Invoice format (e.g. ZUGFeRD 2, XRechnung or Peppol)
• Issue date (in the format YYYYMMDD)
• Invoice number (unique per invoicing account)
• Invoice type (e.g. commercial invoice, credit note, correction)
• Invoice line items (at least one line item with item name, quantity, tax category and price)
• Buyer/recipient address with name, street, postal code, city and country
• Seller address with name, street, postal code, city and country (if not stored in the account settings)

What to do?

Check that all of the fields above are filled in before saving or creating the invoice. A validation error typically indicates which field is empty.

Tax categories and tax rates are combined incorrectly

Each invoice line item needs a tax category (a code such as "S", "Z", "E", "AE") and a tax rate (a numerical value such as 19, 7, 0). These must match.

Standard combinations:

• Category S (standard): for normal VAT rates such as 19 %, 7 %, etc.
• Category Z (zero): for 0 % rates (e.g. books, magazines). The tax rate must be 0.
• Category E (tax-exempt): for tax-exempt services. No tax rate is required here, but a reason for the exemption is.
• Category AE (reverse charge): for reverse charge services (e.g. intra-community services between businesses). The tax rate should be 0.

Example: a common error with credit notes without VAT

If you create a credit note for an intra-community supply (without VAT), the tax category must not be "Standard". Select instead:

• Category "Z" (zero) with a tax rate of 0, or
• Category "AE" (reverse charge) for services under reverse charge conditions.

Only use category "AE" if both parties (seller and buyer) are businesses (with a VAT ID).

What to do?

1. Check the tax category of each invoice line item.
2. Make sure the tax category matches the tax rate (e.g. category "Z" only with rate 0).
3. If you use an exemption (category "E"), store the reason in the invoice settings or directly in the invoice.

Invoice numbers are assigned twice

Each invoice number must be unique in your invoicing account.

When does this error occur?

• You try to create an invoice with a number that has already been used.
• With Peppol delivery, an invoice is blocked if the number already exists, because Peppol uses the invoice number for deduplication.
• For quotes, an error is shown if the quote number has already been assigned.

What to do?

1. Check your existing invoices to see whether this number has already been assigned.
2. Use a new invoice number that has not been used yet.
3. If you generate invoice numbers automatically: check in the invoice settings that number assignment is configured correctly.
4. If you want to create an invoice several times (e.g. because the first one was past its deadline): use a new invoice number.

Buyer/seller data is incomplete (address fields)

The address field of an invoice must contain all required components.

Required address components:

• Name (name of the buyer or seller)
• Street and house number
• Postal code
• City/town
• Country (as an ISO code, e.g. "DE" for Germany, "AT" for Austria)

Common errors:

• The postal code or city is missing.
• The address field is empty or contains only partial information.
• The country is not entered as an ISO code (e.g. "Germany" instead of "DE").
• For foreign addresses: the country was not recognized.

What to do?

1. Check that all address fields are filled in completely.
2. Use the correct format for the country (ISO code, e.g. DE, AT, CH, FR).
3. If you use contacts with foreign addresses: make sure the country is stored correctly in the contact data.

Introduction text is not allowed

The introduction text (the "Introduction" field) is not permitted for certain invoice formats.

When does this error occur?

• You try to create a Peppol invoice with an introduction text.
• The introduction text is too long or contains invalid characters.

What to do?

1. Check whether the invoice format (e.g. Peppol) allows an introduction text.
2. Remove the introduction text or use the invoice's standard notes instead.
3. If you need text at the beginning of the invoice, use the notes field or use a different invoice type.

Reference fields (order number, contract number) are used several times

If you specify the same order number or contract number in several invoice line items, this can lead to validation errors with XRechnung.

When does this error occur?

• You use the same order number (IssuerAssignedID) in several line items.
• You use the same contract number in several line items.

Background:

In XRechnung and other electronic invoice formats, reference fields are unique per invoice line item. Using them several times can lead to conflicts or rejection by recipient systems.

What to do?

1. Check that each invoice line item has its own order number or contract number.
2. If all line items refer to the same order, use a field at the invoice header level instead (buyer reference).
3. Use unique references for each line item.

Preview or PDF export fails

If an invoice preview or PDF export fails with a validation error, there are errors in the invoice structure that the system cannot display.

Common causes:

• Required fields are empty (net and gross amounts cannot be calculated if taxes or totals are missing).
• Tax categories and tax rates are combined incorrectly.
• Calculated amounts (net amount, taxes, gross amount) are contradictory.
• The format does not allow the invoice template.

What to do?

1. Check all invoice line items for complete data (quantity, price, taxes).
2. Check that tax categories and tax rates are combined correctly.
3. Try saving the invoice (without creating it) and see which error is reported.
4. If the preview does not work in draft mode, check the account settings and the invoice template.

Payment reminder shows no preview

If no preview is shown when you create a payment reminder, data in the linked original invoice may be damaged or incomplete.

What to do?

1. Check the original invoice on which the reminder is based.
2. Make sure the original invoice has all required fields.
3. Try creating the reminder with a different original invoice.
4. Contact support if the preview still does not work.

Importing an XRechnung fails even though validation is successful

If you import an XRechnung and receive an error message even though the validation report shows no errors, there can be several causes:

Possible causes:

• The file is damaged or has encoding problems.
• The system could not visualize the file in faktoora (even though the structure is correct).
• There are compatibility problems between the XRechnung version and the faktoora version.

What to do?

1. Check that you are uploading the XML file of the XRechnung (not the PDF).
2. Make sure the file is UTF-8 encoded.
3. Try uploading the file again.
4. If the problem persists, contact support.

Validation errors for country-specific invoice formats (FatturaPA, KSeF, Verifactu)

Invoices for Italy (FatturaPA), Poland (KSeF) or Spain (Verifactu) are subject to special validation rules for tax rates and buyer data.

FatturaPA (Italy):

• Only Italian tax rates are allowed: 22 %, 10 %, 5 %, 4 % and 0 %.
• If you use a different tax rate (e.g. 19 % or 7 %), the invoice is rejected.
• The buyer must have an Italian Partita IVA or a Codice Fiscale.

KSeF (Poland):

• Only Polish tax rates are allowed: 23 %, 8 %, 5 % (with category "S") and 0 % (with category "Z", "K", "G" or "E").
• Reverse charge categories ("O", "AE") are also allowed.
• Other tax rates or categories are rejected.

Verifactu (Spain):

• Special requirements apply to Spanish tax rates and categories.

What to do?

1. Check which tax rates are allowed for the destination country.
2. Use only the permitted tax rates and categories.
3. Consult the documentation for the respective country or contact support.

General tips for avoiding errors

1. Check completeness: before saving or creating an invoice, check all required fields.
2. Use standard formats: use common invoice formats (ZUGFeRD 2, XRechnung, Peppol) with standard tax rates.
3. Avoid duplicates: make sure invoice numbers, order numbers and contract numbers are unique.
4. Validate addresses: check that all address components (name, street, postal code, city, country) are complete.
5. Check account settings: make sure your account settings (tax numbers, bank details, etc.) are correct.
6. Test in draft mode: create an invoice in draft mode (draftOnly) first to detect errors before you send it.