Did you build your native app pointing to your localhost environment or a cloud environment? Make sure you are logging in with a user which is defined for the runtime you are trying to reach, and user/passwords would be different.
Are you able to login to the cloud environment that the APK is pointing to (for example, with an admin account)?
If so, you can create a new user with access to the native (part of the) app (and then you know the credentials for sure!)