I recognize the relevance of having the ability to use electronic signatures in QuickBooks Online, blucrew. I'm here to help find the best options to streamline your activities.

At the moment, QuickBooks Online doesn't have an E-signature feature. This functionality is available via the mobile app, but it's limited to estimates and invoices. Since you're looking for a way for customers to sign documents, such as contracts, a third-party service can be a great solution for those who prefer not to upgrade to QBO Advanced.

For detailed information, you can visit this article for a fast and secure transaction in the mobile app: Capture signatures using the QuickBooks Online app.

I've included a reference document that clearly explains the process for converting an estimate into an invoice: Convert an estimate into an invoice in QuickBooks Online.

I'm just a click away if you need more guidance with your estimate. Simply hit the Reply button below, and I'll be delighted to assist you further. Looking forward to hearing from you!