I want to show my company registration no at invoice. Please help.

Let me guide you on how to add your Company registration number to your invoice, userhuini.

We can turn on the Company registration number (CRN) field on your invoice template. This way, the CRN will show when printing or sending an invoice to your customers. Let me show you how: 

1. Go to the Gear icon on the top menu.
2. Choose Custom Form Styles.
3. Tick Edit on your invoice template.
4. Select Content.
5. Tap the Header part on the sample invoice.
6. Hit the Company registration number link and place a checkmark on it. Then, enter the details on the field. 
7. Press Done.

For more details about this one, see Customise invoices, estimates, and sales receipts in QuickBooks Online article. This also provides details on how you can personalize your sales forms to add info to your business brand in QuickBooks Online (QBO).

Feel free to visit our Manage Customers and income page for more insights about managing your customer transactions.

I hope that this response finds you with a smile. Keep me posted if you need a hand with running your financial reports or any QBO related. I'm always here to ensure your success. Have a great day ahead.