App authorisation works fine within the Unity Editor doesn't work for the executable version

[andioan]

I am using Unity to create an app that fetches data from FitBit for my final year project. Within the editor, when I run the program for the same user the fitbit authorisation is successful, and it takes me to the web-page with the return code within the html I need to use to get the data (image 2). But, when I build and run my .exe, unfortunately the authorisation fails for the same user with the same data. What am I doing wrong? My callback url in my database-code matches the one stored in my fitbit app details, so it can't be that. Do I have to get some sort of permission from fitbit to use a released version of my application? Any thoughts on why this hapens and how to fix it would be really appreciated as my entire dessertation depends on it.