How do we invoice by using two types of invoice forms in quickbook online in a same company for two product lines ?

Thanks for dropping by the Community, @MC121.

To send/email two types of invoices in QuickBooks Online (QBO), you need to create a new template for each of them. The steps to do this are pretty quick and easy.

Here's how:

1. In QBO, go to the Gear icon at the top right to get to the Custom Form Styles. 
2. Click the New style option and pick Invoice in the drop-down. 
3. Adjust the general layout and look of your template in the Design tab.
4. Start customizing the details in the Content tab, then personalise your email message in the Email tab.
5. Hit Done once complete.

To learn more about the process, check out this article: Customise invoices, quotes, and sales receipts in QuickBooks Online.

After that, just click the Customise option when creating an invoice to change the template. 

Reach out to me in the comment section below if you have any other questions or concerns. I'll be here to assist. Have a wonderful day!