I have a creditor that is also a debtor. I need to add them as a creditor, but QBO says I can't because 'another debtor/creditor is already using that name'.

Hi accounts152,

You cannot have the a creditor and debtor with the exact same display name, which is why it's giving you this error.

To resolve this, edit their debtor's display name to something that will identify them as the debtor (e.g. by putting Debtor at the end of their name). Then, when adding them as a creditor, do the same but for creditor. 

Here's an article that details further into how to change the display name: https://quickbooks.intuit.com/learn-support/en-au/manage-suppliers-and-expenses/error-the-name-supplied-already-exists-another-customer-supplier/00/262939

Hope this helps!

Bonny