Error Assigning Supplier Bank Account Owner - 1.The external bank account already exists

I have an existing supplier bank account that I need to assign to another supplier. When I try to do the assignment in the supplier, there are no bank accounts listed.

So, I figured out that I need to assign the supplier as a bank account owner. I went to the primary owner of the bank account and in the Banking Details page, I tried to assign the supplier as an additional bank account owner. When I save it, I receive this error message:

1. The external bank account already exists
2. One of the assignment of this bank account is related to operating unit <OU Name>