Hello there, @ivweld.
Thanks for informing us about having this issue.
Currently, some of our customers experience this hurdle, rest assured, our product engineers are working to fix this as soon as possible. The case code is INV-52004.
Please contact us through the Help icon on the top right and choose either to Start a message or Get a callback. That way, you can be added to users who get this concern and attach your accounts name to the investigation. That said, you'll get notifications moving forward once it's fixed.
Here's how to reach QBO support:
- Sign in to your QuickBooks Online company.
- Select Help (?) at the top right.
- Enter your concern, then select Let's talk.
- Select Contact Us to connect with a live support agent.
- Choose to Start a message or Get a callback.
Please know that they're available from M-F 6 AM to 6 PM PT or chat them through this link.
In the meantime, you can also download the estimate by going to the customer's Transaction List and then open the estimate. From the Estimate window, select Print or Preview, then Print or Preview to Download the PDF file. Once done, you can attach this and email it to your customer through your emailing service.

In case you want to get payments online, you can register to QuickBooks Payments and link it with QuickBooks Online to be paid faster.
Feel free to drop a comment anytime you need assistance with QuickBooks. I'm always here ready to help. Have a safe day ahead, ivweld.