Combine projects to one invoice

Good day, Ela_G.

The option to create a single invoice that covers multiple projects is unavailable in QuickBooks Online. You can only create multiple transactions under a single project in the system.

You may consider looking for a third-party application that can add multiple projects to a single invoice. Here's how:

1. Go to Apps on the left pane.
2. Click Finds Apps.
3. Type a keyword in the Search for an app field.
4. If you have found the app you're looking for, click Get App Now.

Also, you can learn more about the fundamentals of using this feature, you can go through these helpful articles: 

• Set up and create projects in QuickBooks Online.
• Projects FAQ.

I'll be right here if you need more help, @Ela_G. Have a great day!