I'm here to ensure you can convert your estimates to invoices seamlessly in Quickbooks Online. Firstly, I would like to know further details regarding the error message you've received while performing this task. I would also appreciate it if you could post a screenshot of this. Doing so will help us find an appropriate resolution to this concern.
In the meantime, let's perform some troubleshooting steps to determine if this issue is browser-caused. I recommend logging into your QBO account in another browser by using an incognito browser.
Here are the keyboard shortcuts you can utilize depending on the browser you are using:
For Microsoft Edge, press Ctrl + Shift + P.
For Safari, press Command + Shift + N.
For Firefox, press Ctrl + Shift + P.
If the private browsing session doesn't work, you can clear the browser's cache so the system can restart. Also, you can use up-to-date browsers to maximize your QBO experience.
Don't hesitate to contact us if you have further concerns about converting estimates to invoices in QBO. The Community forum is always available to assist you.