Can I upload a journal entry using excel? I have a long transaction list that I want to post, and it would be great if I can do it using excel.

A warm welcome to the Community, @nelly11. 

I understand the significance of uploading a journal entry using Excel. Uploading it isn't possible in QuickBooks Online (QBO). I suggest using a third-party app to complete this process. Also, these are the possible data that you can import: 

• Bank Data
• Customers
• Vendors 
• Chart of Accounts 
• Products and Services 
• Invoices. 

I'm also sharing this article on how to reverse a journal entry: Reverse or delete a journal entry in QuickBooks Online.

You can always visit the Community forum if you have questions regarding journal entries. We're always glad to help you.

@nelly-durango-cd 

You need to use an importer tool

https://get.transactionpro.com/qbo