3801790 - Error: "This email address has already been used" in SAP Ariba Invoicing when configuring email in Configure Inbound Email app

I am trying to configure a new inbound email address in the Configure Inbound Email application in SAP Ariba Invoicing. When I enter an email address prefix (e.g., 1000) and save, I receive the error:

This email address has already been used.

The email prefix is not currently configured for any Company Code in my tenant. 

- SAP Ariba Invoicing
- Configure Inbound Email application

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