One of my contractors is trying to set up his intuit account but the system dosen't let him. It says HTTP Status 400 - Bad Request. Thanks in advance

You can send another invitation to the contractor, @userchristopher-rodr.

Let's isolate the error you're having by resending the email invitation to your contractor. Once they received the email, try to let them create the account using the link of the new email invitation. 

Here's how:

1. Go to the Payroll or Workers menu and proceed to the Contractors tab. 
2. Click the name of the contractor. 
3. At the upper part of the page, hit the Send a reminder or Send email link. 
4. Select Send.

See this article for more information: Invite a contractor to add their own tax info.

You can also refer to this article for more information on how to add, edit and inactivate contractors

Feel free to leave a reply if you need any further assistance in setting up your contractor's profile. I'd be around to assist. Have a great day!