How can i restore the automatic journal entry numbering ?

Edit, Preferences, Accounting, Company Preferences, Check off Automatically assign journal entry number.

Hi there, 

You've come to the right place for help. I got your back. 

It's important you have control of the Journal Entry number and I have just the answer you're looking for. First, you'll need to disable the Custom transaction numbers feature through your Settings. Here's how:

1.    Click the Gear icon, then select Company Settings.
2.    Click on the Sales form on the left.
3.    Then click the edit icon for Sales form content.
4.     Uncheck the checkbox labelled Custom transaction numbers, and click Save.

After turning off Custom Transaction Numbers setting on QB Online, Invoice numbers will be automatically incremented when you send invoices to QB Online. If you want to turn on Custom Transaction Numbers setting go through the steps and check the Custom Transaction Numbers checkbox and Save.

If you need Help or further assistance, don't hesitate to reach back to me.