In order for the FglAM launcher to be able to control the service, it needs to know what it is configured service-name is. This value is defined as part of the FglAM configuration, and is used by the launcher when it creates (via fglam.exe --install-service) or removes (fglam.exe --remove-service) the service.
When registering the FglAM install as a service directly via the Windows 'sc' process, you must use the same service name that FglAM would have used if the "--install-service" option was used. If you choose something different to register the service name under and you later ask the FglAM process to stop the service; it expects that the service-name is 'FglAM' and it tries to stop that service. It has no idea that the service it is supposed to be able to control was registered by another process and gave it an arbitrary name.