@STAC98 said:

So i am trying to test out the API using POSTMAN and the testing options under the documentation, but I am given an error code and the message, "Invalid API key: You must be granted a valid key." However the example API request above works fine on POSTMAN.

It's not clear to me which documentation you are refering to, TMDB or POSTMAN? If using the TMDB doc "Try It!" button, you have to be logged in (upper right corner of the page) and select "Access Token Auth", -not- "API Key Auth" for the authorization header.