Hello, How to change heading of TAX INVOICE TO INVOICE

If you want to change the invoice header, all you need to do is tweak the template you're using, Shailesh. Don't worry, I'll be right here to assist you every step of the way.

Open the Custom form styles page to look for that template. Here's how:

1. Click the Gear icon and select Custom form styles.
2. From there, locate the invoice template and select Edit.
3. Select the Content tab and click the Header section.
4. In the Form part, remove the "Tax" text in the Tax invoice field and leave only the "Invoice" text.
5. Once done, select the Preview PDF to check the changes.
6. When everything is all right, click Done. 

For reference, read this guide: Customise invoices, estimates, and sales receipts in QuickBooks Online.

Always make sure to select this template every time you make an invoice. For easy identification, enter a simple name in the designated field under the Design tab.

When everything is in order, you can refer to this resource to help you keep track of your customer's payments: Record invoice payments in QuickBooks Online.

Feel free to reach out again if you need further help with modifying your invoice template. Just drop a message here. I'll ensure everything is sorted out for you. Have a good one.