## Why change Invoice Numbers?
> Xero enforces a strict rule: Every Invoice Number must be unique.
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### 📍 **Where to find this setting?**
Go to **Settings → Integrations**. On the **Xero** card, click **Settings**. Scroll down to the **Field Format Settings** section.
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## Go to **Field Format Settings**
To customize these fields, click inside the box and type the **@** symbol. This will open a dropdown menu where you can select the available **Tags**.
### Here is a recommended setup to ensure unique invoice numbers:
- **Sales Order Invoice Number:**
- _Configuration:_ Type `@` and select **Order Full Number**, type a hyphen `-`, then type `@` and select **Order Date (YYMMDD)**.
- _Result:_ Creates a unique ID like "**POS-1001-251128**". This includes the sales channel code, order number, and date to prevent duplicates.
- **Sales Order Reference:**
- _Configuration:_ Type `@` and select the **Order Number** tag.
- _Result:_ This puts the simple order number (e.g., "**1001**") in the "Reference" column, making it easy to search for in Xero.
Do not manually type the tag name (e.g., do not type Order Number). You must use the @ menu to select the official tag from the list. If you type the text manually, the system will not recognize it as a variable and will just print the plain text on your invoice. If the **Sales Order Invoice Number** has text but no tag, it can't be saved.
Don't forget to type a separator (like a hyphen - or a slash /) between your tags. This makes the final invoice number much easier to read (e.g., POS-1001 is better than POS1001).