the URL used in function getActivityDetails is invalid and results with HTTP error 404, please correct it
from:
$strResponse = $this->objConnector->get("https://connect.garmin.com/proxy/activity-service/details/" . $intActivityID);
to:
$strResponse = $this->objConnector->get("https://connect.garmin.com/proxy/activity-service/activity/" . $intActivityID . "/details");