So how do properly setup a Redirect Uri?

A few days ago, I was playing around with a local API(not Google) and it required me to provide a Redirect Uri while trying to setup my app in their dashboard.

I did some googling and top searches led me to oAuth2.0 and Google Developer's website. But this API I'm using is not related with any of Google's so I thought it won't be relevant.

Is the setup of Redirect Uri for most APIs universal or almost the same? What programming languages can I use to implement this? The description also says I need to parse a subscriber_number and access_token in JSON format. How do I do that?

Please note that I have already found a free hosting site via Firebase and have provided my own link. I also did the initial steps from another user to fire the required access_token that I needed to parse from the Redirect Uri. But accessing it from the browser right after triggering doesn't give me anything. I'm so clueless. Any help is much appreciated!