Customers Applying To Be Vendor Error

Has anyone else had this problem? We followed the steps in this article: https://docs.cs-cart.com/latest/user_guide/users/vendors/allow_customers_to_apply_for_vendor_account.html

...but when someone that already has a customer account applies to be a vendor it returns an error that the "username/email already exists".

Is there a setting I'm missing to ensure someone that opened a customer account can still create a vendor account?

Thanks for anyone who might know this answer.