How do I permanently add HST number in all my invoices, so I dont have to put it each time while invoicing?

At the moment, the option to add your HST number to your invoices permanently is unavailable. I can guide you on how to send a request for this feature, mumtaz,

To make the program better, you can send feedback to let our product team know how this is useful for your business.

1. Navigate to Settings and select Feedback.
2. Provide your comments or product suggestions. Then click Next to submit feedback.

Your valuable feedback will enhance your experience in our ongoing improvement efforts in QuickBooks Online.

To find out how to set up your sales tax collection, please refer to this informative article: Set Up Where You Collect Sales Tax in QuickBooks Online.

Furthermore, for guidance on completing your tax setup and electronically paying your taxes, I've added this article: Pay and File Payroll Taxes and Forms Electronically in QuickBooks Online Payroll.

Let me know if you have any concerns or questions about taxes or if you need assistance adding them to your invoice. I'm here to help and would be happy to assist you.