Once I convert an estimate into an invoice and save it. Why can't I change the quantities or pricing of an item?

Hey there, fsgppromo. 

Thanks for dropping by the Community. I'm more than happy to provide some insight into this, it can be for a number of reasons but most commonly it's because of the status applied to the estimate. When you convert an estimate to an invoice, it needs to be either Accepted or Pending. Below, I'm attaching the steps you can follow to properly convert an estimate to an invoice. 

1. Go to the Sales menu and select All Sales.
2. Find and open the estimate.
3. Select Create invoice.
4. Add more details to the invoice as necessary, then select Save and close.

If you have any other questions, feel free to post down below at any time. Thank you and have a nice day.