How to add vat registration number to invoice template ?

Welcome to the QuickBooks Community, @stuapps87-gmail-. 

Adding your VAT number to invoices is easy with QuickBooks Online (QBO).

To get started, you'll need first to enter your VAT registration number on your VAT centre. Once done, this will automatically be populated when you run invoice preview. Here's how:

1. Go to the Taxes menu and choose VAT.
2. Click the Edit VAT dropdown and select Edit settings.
3. From the VAT registration number field, enter your information.
4. Once done, click Save. 

Next, let's check your invoice template settings to see how the VAT registration number will populate. Let me guide you how:

1. Navigate to the Gear icon and select Custom form styles.
2. Click the Edit button on the template you use. 
3. Go to the Content tab and click the Header.
4. It will show how the VAT registration number is displayed on the invoice. See the screenshot below for your reference: 

Then, you can generate an invoice and select the Print and preview option to check your VAT registration number. 

For more information about modifying your invoice forms, check out this link: Customise invoices, estimates, and sales receipts in QuickBooks Online.

You may also want to run the  Accounts Receivable ageing summary report to have a list of your customers’ outstanding balances. This will show you how much are still due and how long they're past due.  

Keep me posted if you have any other questions about adding your VAT registration number to your invoices. I'm ready to help in case you need one. Have a nice day ahead.