Freshdesk API - Ticket reply from user

I am attempting to utilize the “Create a Reply” endpoint from the Freshdesk API to send a reply to a ticket using a user’s email as identification. I have already successfully utilized the “Create a Ticket” endpoint to generate a ticket with the user’s email. However, when I attempt to use the “Create a Reply” endpoint with the same email, I receive an error message as shown below:


The error message itself is clear, but the limitation is not. Is there a way to accomplish this without having to configure every contact individually? What would be the best way to achieve this?