Unable to add my vat number to invoice header

Hi there, 9130349898672666.

Welcome to the QuickBooks Community. I'll ensure to share details so you're able to add the vat number to the invoice header in QuickBooks Online. 

You can add your vat number as Company Registration Number to the invoice header. To do this, you'll have to create a custom form style for the invoice to checkmark and enter the VAT number in the field I mentioned.

Here's how:

1. Go to the Gear icon ⚙ and select Custom Form Styles.
2. Click the New Style drop-down button.
3. Choose Invoice.
4. Go to the Content tab. Then, click the header part.
5. Click the Company Registration Number link.
6. Enter your Vat number and make sure to checkmark the box.
7. Hit Done.

For additional information, you can click this article: Customise invoices, estimates, and sales receipts in QuickBooks Online.

Once done, use this custom form style or select this template every time you create an invoice. This is to make sure that your VAT number always appears in the entry.

However, if you're unable to perform the steps above, it could be the cache full of history and temp files caused unexpected behaviors. With this, I recommend logging in to your QuickBooks account using a private browser. This is to rule out the possibility of a webpage issue, and private browsing doesn't store local files or cache.

Use these keyboard shortcuts based on the browser you're using.

• For Firefox or Microsoft Edge, press Ctrl + Shift + P.
• For Chrome, press Ctrl + Shift + N.
• For Safari, hold down Command + Shift + N.

If it works in incognito, I recommend clearing the cache of your regular browser. This removes the history or log of sites so you can start with a clean slate. You can check this article to see the steps: Clear cache and cookies to fix issues when using QuickBooks Online.

If the steps above didn't work, use another supported browser as alternatives.

Please refer to this article to view different information on how the Sales page gives you a great at-a-glance view of the status of sales transactions, open invoices, and paid invoices: View sales transactions.

Let me know if there's anything else you need help with. Know that I'm always here to help you anytime. Take care and keep safe!