appium test on saucelabs using serenity framework

Question

i am trying to run appium test on saucelabs using serenity framework. I keep getting the following error;

Caused by: net.thucydides.core.webdriver.DriverConfigurationError: WebDriver was unable to create a new instance of type class io.appium.java_client.AppiumDriver

my serenity.conf is ;

serenity {
take.screenshots = AFTER_EACH_STEP
}

environments {

sauceLabsAppAndroid {

  webdriver.driver = appium
  appium.platformName = Android
  appium.hub = "https://ondemand.eu-central-1.saucelabs.com:443/wd/hub"
  appium.automationName = "UiAutomator2"
  appium.platformVersion = "12.0"
  appium.deviceName = "Android GoogleAPI Emulator"
  appium.app = "storage:filename=app.apk"
  appium.unicodeKeyboard = true
  appium.resetKeyboard = true
  appium.fullReset = true
  appium.sauce.username = "Myusername"
  appium.sauce.accessKey = "MyKey"
  appium.sauce.options.build = "buildversion"
  appium.sauce.options.name = "Test mobile 1"
  appium.sauce.options.deviceOrientation = "PORTRAIT"
  appium.autoGrantPermissions = true
  }
}

what am i doing wrong here