Why do I need to buy an expensive upgrade to UNDO items that did not transfer to the app/online versions properly?

Thanks for checking this out in the Community, Angela.

The old clients might have been activated during the conversion process. No worries, I'll share the steps on how to clean up your client list. 

You can run an unbilled report, Then, uncheck the billable box on each of the transaction so you can make the clients inactive again. Here's how:

1. Go to the Reports menu and type in Unbilled Charges in the Search bar.
2. Once you open the report, you will a list of all unbilled charges.
3. Click on each one of them to open the transaction. 
4. Look for the billable expense link and click on it.
5. Uncheck the Billable box and click Save and close. 

Follow the same steps for the rest of the transactions. Let me also this article for additional details:

• Learn How Features and Data Move From QuickBooks Desktop to QuickBooks Online
• What To Do After You Move From QuickBooks Desktop for Windows or Mac to QuickBooks Online

Let me know if you're able to inactivate old clients after following all the steps. You can also ask follow-up questions in your reply if you need anything else. 

Consider running the Condense Data utility to delete old data before converting it to QB Online. You'll secure the original company file (and backup file) as archives later. You can use the trial version for QB Desktop to open them in the future. 

https://quickbooks.intuit.com/learn-support/en-us/help-article/data-utilities/use-condense-data-util...

You will convert the condensed company file to the new QBO account. You cannot purge Simple Start and you must signup a new one. Don't forget to cancel the old one.

https://quickbooks.grsm.io/US

As an additional option, you can signup a separate Melio account for free to manage and pay your bills to vendors and contractors. You will register the transactions manually in Simple Start.

https://affiliates.meliopayments.com/pricing