I need the VAT number to show on the tax invoice this is a requirement in Zambia.

I understand the importance of showing your VAT on your invoice, contact-electpow. 

In QuickBooks, you can use the Custom field to add some functions that you want to see in your sales form. Since you want to see your  Value-Added Tax (VAT), you can do it by creating a custom field and for it to show in your tax invoices.

Here's how:

1. Go to the Gear and click Custom form styles. 
2. Press the New style dropdown located at the upper right side and then choose Invoice.
3. You'll see that there are three tabs, choose the Content tab.
4. Click the Header section located at the top part of your sample invoice. 
5. At the bottom, you'll see the name Manage custom fields that were aligned with Custom fields.
6. You'll be routed to the Customer fields. Click the Add Custom Fields button. 
7. You can add your custom field and name it according to your preferences. 
8. Tick the box for the All Sales form and turn it on or select Print on the form. Then click Save.

After creating a Custom field for your VAT number, you'll just have to type it as you create your invoice. 

You may also want to utilize this guide to learn how to personalize and add specific info to your sales forms:

Customise invoices, quotes, and sales receipts in QuickBooks Online

We're always here if you have further questions about the VAT number. Have a good day and stay safe.