How can I import existing transactions like Estimates, Bill and Invoices into a new project in QBO without having to create them from scratch?

I hope you're enjoying the day. 

To clarify, are you using QuickBooks Online Advanced? Are you importing these transactions from your bank or another resource? 

Note: You're only able to import transactions in QuickBooks Online advanced. 

On the other hand, you can add existing invoices and estimates to projects. Please note: The best time to add existing invoices to projects is before they're paid. Adding a paid invoice will disconnect the attached payment and will change the status of the invoice to unpaid. For a future reference, while I await your response, I'm including a few articles to help you along the way. 

• Set up and create projects in QuickBooks Online
• Import transactions from other sources
• Import bank transactions from .CSV to QuickBooks

Please let me know if you have further questions or concerns. I'll be here for you every step of the way. You can always reach out to us here in the Community anytime you need a helping hand. Take care! 

@jalhafi 

"How can I import existing transactions like Estimates, Bill and Invoices into a new project in QBO without having to create them from scratch?"

Unfortunately, you can't import such transactions into Customer: Project level in QBO. You may be able to import from the 3-rd party paid app but at the customer level but not into Project.

With QBO, you can import Invoices though. But still, you can import it to a Customer level only (no sub-account or project). After import, you can manually change Invoice to a Project you want.

(Gear icon on top > Tools > Import Data > Invoices).

Hope this helps!

@jalhafi 

Project feature in QBO has limited options. Consider having a project management app and integrate it with your QBO.