Is it possible to sync an invoice (via API) with the same docNumber twice to QBO ending up with two invoice objects in QBO's side?

Let's see what we can do about this, ofir-tehila-work.

In the Community, we won't be able to tell you whether this is possible or not when dealing with APIs. However, we can route you to the Intuit Developer page. This is where APIs and other third-party applications concerns are posted. We have engineers, developers, QuickBooks users, and other third-party application users that might be able to share their experience regarding your concern.

1. Go to this link: https://help.developer.intuit.com/s/.
2. Select QuickBooks Online and click the Ask a Question button.
3. Enter the details of your concern just like how you did in the Community page.
4. Click Ask.

They will jump in to your post and will provide the necessary details that will help you get through with the scenario.

Keep us posted so we can assist you in managing your transactions in QuickBooks.