Cannot insert some products onto a new invoice under the product/service option, how do I correct this?

I know how this process takes time when you're unable to enter a product/service item into QuickBooks Online (QBO). We'd want to make sure that we get this sorted out, lisa-copperrepub.

To figure this out, we can run some basic troubleshooting tests. Open a private browser and create another invoice to see if you can select a product item this time. The private mode prevents the cache from being retained while the website is up and running, which may cause issues. Here's a list of shortcut keys that you can use to get to one:

• Ctrl+ Shift + N for Google Chrome
• Ctrl + Shift + P for Mozilla Firefox and Microsoft Edge
• Command + Shift + N for Safari

Then, an create an invoice again. Let me guide you on how: 

1. Click the + New Plus icon. 
2. Select Invoice.
3. From the Customer dropdown, choose a customer. Make sure all of their info is correct, especially their email address.
4. Review the Invoice date. If you need to, change the due date in the Terms ▼ dropdown.
5. From the Product/Service column, select a product or service. You can also select +Add new to create a new product or service right from the invoice.
6. Enter a Quantity, Rate, and Amount if needed.
7. Choose a VAT option. If you are unable to see tax, make sure you have set up tax.
8. Press Save and close.

If this works, go back to the regular browser and clear the cache to refresh the background process of your browser settings. But, if the same thing happens, use another supported browser. 

Feel free to visit the Invoices and payments page for more insights about adding, organising, and sending invoices.

Don't hesitate to click the Reply button below if you have follow-up questions on this matter or referring to something else. Please know I'm always around to help with any QuickBooks issues you may be having. Take care always.