We're glad to see you here in the Community, @abaldi-contrasti. I can assist you with enabling the Review and Approve button when sending estimates in QuickBooks Online (QBO).
When creating an estimate, make sure that you select the Modern option in the Design section. It will enable the Review and Approve button when your customers receive estimates.
Here's how:
- Sign in to your QBO company.
- Go to the Sales tab and select Create Estimate.
- Fill out the required details for the estimate.
- Click on the Manage option.
- Select the Design dropdown, then tick Modern.
- Once everything is ready, click Review and Send.
I've also attached a screenshot for your reference:
![image.png image.png](https://quickbooks.intuit.com/learn-support/image/serverpage/image-id/100796i2C6FEFB8E97DE324/image-size/large?v=v2&px=999)
After your customer accepts your estimate, you can convert it into an invoice by checking this article: Learn how to convert an estimate into an invoice in QBO.
Please comment below if you need further assistance with estimate emails or have any QuickBooks concerns. Take care always.