Thanks for joining us here in the Community, @Nishad Maheen.

Allow me to share some insights on how you can have the VAT number to appear on your invoices in QuickBooks Online.

As mentioned by my colleagues above, the VAT number will show up automatically on the invoices after entering the registration number upon setting up VAT.   

These are the steps that you'll need to take during the set up:

1. On the left panel, click VAT.
2. Select on Set up VAT.
3. From the Set up VAT page, choose the Start of VAT period, Filing frequency, Reporting method, and your VAT Registration No..
4. Click Next.
5. Hit on Got it.

If the registration number is still not showing, I suggest checking the set up of the invoice template that you're using. Utilizing a customized template can be the reason VAT numbers are not displaying on the invoice.

Here's a link that you can check out about the different customization that you can do for sales forms in QBO: Customise invoices, estimates, and sales receipts in QuickBooks Online.

If doing this doesn't make a difference, I recommend contacting our Customer Care Team. They have the tools that can help further isolate this matter and identify its root cause. They can also create an investigation ticket if necessary.

You can also check out these links below about adding and removing VAT rates in QBO for your reference:

• How do I set up sales GST/VAT rates and use them on forms? (International QBO)
• Remove a VAT or GST rate

Know that my doors are always open to help if there's anything else that you need. Thanks for coming, and have a great week.