SAP Build Apps BTP Destination Not Working When Deployed - Works in Preview

[tokgozatakan]

I have created the destination shown below, then connected it to Build Apps via Universal REST API integration. 

It works well when I click on test, or in the preview. 

However, when I deploy it and open it, the destination returns 500 without any explanations. 

Has anyone come across a similar issue? 

[tokgozatakan]

When I checked the application logs, I can see the error coming from the destination.

Retrieval of OAuthToken failed due to: Unable to fetch refresh token from the specified token service URL. Response was: Bad credentials

I am able to replicate the same issue with postman:

The credentials are actually correct, I am able to get bearer token from my other OAuth2SAMLBearer destination for another system.