Solution
The constant (CockpitApplicationName) must be set to the "Internal Name" of the app under which the app was registered in the Developer Cockpit. This can either be done directly in the app by overwriting the value or by creating a Cloud Foundry environment variable via manifest:
env:
MX_MindSphereSingleSignOn_CockpitApplicationName: NAME_OF_THE_APP
NOTE: Make sure to "Commit" your changes in the Mendix Modeler before publishing your application to Mindsphere
Notes