You just need to call mFusedLocationClient.removeLocationUpdates(mLocationCallback) in onPause() of your Activity. However, there is a bit more to it than just that.

Use member variables for the FusedLocationProviderClient and LocationRequest in your main activity:

import com.google.android.gms.location.FusedLocationProviderClient;
import com.google.android.gms.location.LocationCallback;
import com.google.android.gms.location.LocationRequest;
import com.google.android.gms.location.LocationResult;

public class MainActivity extends AppCompatActivity
        GoogleApiClient.ConnectionCallbacks,
        GoogleApiClient.OnConnectionFailedListener {

    FusedLocationProviderClient mFusedLocationClient;
    LocationRequest mLocationRequest;

    //..........

Use a member variable for the LocationCallback as well:

LocationCallback mLocationCallback = new LocationCallback(){
    @Override
    public void onLocationResult(LocationResult locationResult) {
        for (Location location : locationResult.getLocations()) {
            Log.i("MainActivity", "Location: " + location.getLatitude() + " " + location.getLongitude());

        }
    };

};

Then, assign mFusedLocationClient in onCreate() :

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    mFusedLocationClient = LocationServices.getFusedLocationProviderClient(this);
    requestLocationUpdates();

    //...............
}

Then in onResume(), if theFusedLocationProviderClient is set up, then use it.

@Override
public void onResume() {
    if (mFusedLocationClient != null) {
        requestLocationUpdates();
    }
}

public void requestLocationUpdates() {
    mLocationRequest = new LocationRequest();
    mLocationRequest.setInterval(120000); // two minute interval
    mLocationRequest.setFastestInterval(120000);
    mLocationRequest.setPriority(LocationRequest.PRIORITY_BALANCED_POWER_ACCURACY);
    if (ContextCompat.checkSelfPermission(this,
            Manifest.permission.ACCESS_FINE_LOCATION)
            == PackageManager.PERMISSION_GRANTED) {
        mFusedLocationClient.requestLocationUpdates(mLocationRequest, mLocationCallback, Looper.myLooper());
    }
}

And finally, in onPause(), call removeLocationUpdates():

@Override
public void onPause() {
    super.onPause();
    if (mFusedLocationClient != null) {
        mFusedLocationClient.removeLocationUpdates(mLocationCallback);
    }
}

According to the documentation, the getCurrentLocation() takes two parameters.

The 1st parameter it takes is the priority (e.g. PRIORITY_HIGH_ACCURACY) to request the most accurate locations available, or any other priority that can be found here.

The 2nd parameter it takes is a cancellation token that can be used to cancel the current location request.

From the Google play services reference, a CancellationToken can only be created by creating a new instance of CancellationTokenSource.

so here is the code you need to use when using getCurrentLocation()

class YourActivity : AppCompatActivity() {

    private lateinit var fusedLocationClient: FusedLocationProviderClient

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.your_layout)

        fusedLocationClient = LocationServices.getFusedLocationProviderClient(this)

        fusedLocationClient.getCurrentLocation(LocationRequest.PRIORITY_HIGH_ACCURACY, object : CancellationToken() {
                override fun onCanceledRequested(p0: OnTokenCanceledListener) = CancellationTokenSource().token

                override fun isCancellationRequested() = false
            })
            .addOnSuccessListener { location: Location? ->
                if (location == null)
                    Toast.makeText(this, "Cannot get location.", Toast.LENGTH_SHORT).show()
                else {
                    val lat = location.latitude
                    val lon = location.longitude
                }

            }

    }
}

Instead of getting the last known location, you can get location updates in specific intervals. Here is the code.

Declare these fused location provider class and location callback class

private var mFusedLocationProviderClient: FusedLocationProviderClient? = null
private var mLocationRequest: LocationRequest? = null
private var mLocationCallback: LocationCallback? = null  
private const val LOCATION_REQUEST_INTERVAL: Long = 5000

`

Here is the necessary method for the location request

private fun createLocationRequest() {
    mLocationRequest = LocationRequest.create()
    mLocationRequest!!.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY)
    mLocationRequest!!.setInterval(LOCATION_REQUEST_INTERVAL).fastestInterval =
    LOCATION_REQUEST_INTERVAL
    requestLocationUpdate()
}

private fun requestLocationUpdate() {
    if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION)
        != PackageManager.PERMISSION_GRANTED ) {

        Log.e("permission", "denied");


        // TODO: Consider calling
        //    ActivityCompat#requestPermissions
        // here to request the missing permissions, and then overriding
        //   public void onRequestPermissionsResult(int requestCode, String[] permissions,
        //                                          int[] grantResults)
        // to handle the case where the user grants the permission. See the documentation
        // for ActivityCompat#requestPermissions for more details.
        return
    }

    mFusedLocationProviderClient!!.requestLocationUpdates(
        mLocationRequest,
        mLocationCallback,
        Looper.myLooper()
    )
}

Then call these "createLocationRequest" method and location callback classs in onCreate().

    mFusedLocationProviderClient = LocationServices.getFusedLocationProviderClient(requireContext())

 createLocationRequest()
 mLocationCallback = object : LocationCallback() {

        override fun onLocationResult(locationResult: LocationResult) {
            super.onLocationResult(locationResult)
             val lat  = locationResult.lastLocation.latitude
             val lng = locationResult.lastLocation.longitude
                                
     
        }
    }

And remove location update listener in onPause() or onDestory() as per your requirement.

    mFusedLocationProviderClient!!.removeLocationUpdates(mLocationCallback)