Unable to invoke POST WEBAPI from PostMan

Hi reader!

I configured an post API (whose purpose is to write in database from outside Appian) which works well when I test it inside Appian. When I try to invoke the API outside Appian (that is through PostMan), it throws Error 500 - Internal Server Error. I have used basic authentication in PostMan Authentication. The user possessing this credential, is being made as the Administrator of API, data store and other required objects. 

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