App unable to make invoices. Please help!

I'm here to make sure you're able to create invoices in QuickBooks, @usersales7.

We can perform some troubleshooting steps to fix this. There are times that the browser is full of frequently accessed pages, thus causing some unusual responses. 

First, clear the app's cache files. Doing so helps in fixing any sorts of errors in the system. Here’s how to do that:

1. Open your QuickBooks app.
2. Go to the Help menu at the top of the screen.
3. Click the Rest App Data option on the drop-down selection.

If you get the same result, uninstall and reinstall the QuickBooks Online app. This is to ensure you get the most recent version of the application. 

In the meantime, you may consider creating an invoice in a web browser. Here's how:

1. Go to the + New button and then select Invoice.
2. From the Customer ▼ dropdown, choose a customer. 
3. Review the Invoice date. Then from the Terms ▼ dropdown, select the due date.
4. From the Product/Service column, choose a product or service. 
5. Enter a quantity, rate, and change amount if needed.
6. When you're ready to send the invoice, select Save and send.

For more information, feel free to visit this article: Create invoices in QuickBooks Online.

You'll want to personalize your invoices, here's how to create custom templates.

Feel at ease to comment down below if have other concerns with QuickBooks. I'll be around to help you out. Have a great day ahead.