making a subcontractor an employee QBO doesn't let me enter the same name twice

Thank you for dropping by the Community today, DD0225.

Switching someone from a subcontractor to an employee can be challenging when you're unable to perform the task seamlessly. It's important to maintain the historical payment information while also setting up the individual as an employee. Let's work together to find a solution that meets both requirements.

The issue you encounter indicates that the name supplied already exists. We'll have modify the name of the employee so you can the name seamlessly. For example, add a middle initial or a [1] at the end.

This process ensures that you can include the person as an employee without creating a duplicate entry. You can take a look at this article for more details: Fix "the name supplied already exists" error message in QuickBooks Online.

To set up the worker:

1. In your company, navigate to the Payroll menu on the left panel and choose Employees.
2. On the Payroll page, click the Add an employee button.
3. This will open a screen that lets you input the worker's name, and email address. 
4. If you wish to to enter their own personal, tax, and banking information, uncheck the Yes, allow employee to enter their tax and banking info in Workforce box and tap the Continue button. 
5. In the Employee List screen, enter the worker's information.
6. Press the Save button. 

For more in-depth information, take a look at this article: Add your new employee to QuickBooks Payroll. It includes instructions on on how to invite your employee to input their own data.

If you wish to edit your employee or vendor's information, as well as organizing your lists, the following resources will direct you through the entire process:

• Add a vendor in QuickBooks Online
• Edit or change employee info in payroll
• Merge duplicate accounts, customers, and vendors in QuickBooks Online

If have questions on how to set up your employee's information or concerns about this matter, let me know in the comment section below. I'll get back to make sure everything is taken care of for you. Enjoy the rest of the day. 

Rename your sub in the vendor list (and "sub" next to his name or a 1) and then you will be able to add the name into the employees list.