One common error that is encountered when first trying to sync invoices between P3 and QuickBooks Online (QBO) is the following:

Operation Create/Update with Deposit turned off from Sales Deposit preference is not supported

If you receive this error, then you must turn on Deposit setting within your QuickBooks Online Account.  Here are the instructions on how to do so:

1) Login in QBO

2) Click the Gear Icon in the Upper Right Hand Corner

3) Select Account and Settings

4) Select Sales

5) In the "Sales form content", enable the "Deposit" setting.

Screenshot of Account and Settings Page