When converting an estimate to invoice I keep getting an error message saying ‘invoice has to be linked to sales line’ what does this mean?

Hello, @jhpaintworx.

Let's first delete the estimate you're currently working on. Once complete, let's access your QuickBooks Online account using a private browser. This is to isolate the error for a possible browser-related.

Here are some keyboard shortcuts you can try:

• For Chrome, press Ctrl+Shift+N. 
• For Internet Explorer or Firefox, press Ctrl+Shift+P.
• For Safari, hold down Command+Shift+N.

Once logged in, let's recreate the estimate and convert it to an invoice. If you're able to proceed without any error, I'd recommend clearing your regular browser's cache. Also, to check any issues with your browser’s health and its compatibility with QuickBooks Online, you can run the Browser Health Checkup Tool.

Keep me posted if you have other questions. I am always here to help.