How do i fix this problem in QB invoicing? When I checkmark the tax on a line item it changes the amount to $0.00 for that line. Never had this happen before.

I would be glad to share some information with you regarding the invoicing process in QuickBooks Online (QBO), Gilarepair.

QBO offers functionality that enables the creation of invoices, allowing you to finalize and compute the rate established with tax for your client.

When ticking the tax checkbox, the item amount should not be zeroed out. As you've encountered an unexpected behavior. I recommend preforming browser troubleshooting to identify and rectify the problem.

Start by creating your invoices using an incognito window. This mode doesn't save your browsing history, cookies and site data. These are the keyboard shortcuts to open the window:

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

If it fixes the issue, go back to the regular browser and clear the cache. If the same thing happens, have your customer use other supported browsers and ensure they're up to date.

Also, I've added these articles to help you maximize your experience with your invoices, estimates, and financial reports in QBO: 

• Convert an estimate into an invoice.
• Run reports in QuickBooks Online.

Please do not hesitate to reach out to me at any time if you have any inquiries regarding invoices. I am here to assist you. Best regards!