🧾 How Prefix and Postfix Validation Works for Invoice Numbers

To help keep your invoices organised and avoid confusion, the system includes built-in protections around invoice number prefixes and postfixes.

Here’s a simple explanation of how it works:

✅ What You Can Do

You can successfully create or edit invoice numbers as long as the prefix and/or postfix you use is unique.

Here are some actions that are allowed:

• ✅ Create an invoice number using a brand-new prefix or postfix that hasn’t been used before.
• ✅ Add a unique prefix or postfix to an existing invoice number that didn’t have one previously.
• ✅ Rename a prefix or postfix back and forth within the same invoice number (e.g., from TEST1 to TEST2, then back to TEST1).
• ✅ Change the letter casing of a prefix/postfix on the same invoice number (e.g., from TEST to test).

❌ What’s Not Allowed

To avoid duplication, the system blocks changes where the prefix or postfix:

• ❌ Exactly matches an existing one already used on another invoice invoice number (e.g., reusing TEST on a different invoice number).
• ❌ Matches a previously used one, even if the casing is different (e.g., trying to use test when TEST already exists on a different invoice number).

When this happens, you’ll see a warning message and won’t be able to save the invoice number.

📷 Example of blocked renaming:

🔍 How the System Checks for Duplicates

• The system treats prefixes and postfixes as case-insensitive when checking for duplicates. This means Test, TEST, and test are all considered the same.
• For Hungarian invoice submission to NAV, casing does not matter either — NAV does not differentiate between uppercase and lowercase letters. So changing the letter case will not cause any issues with the invoice serial number.
  
  

📝 Summary