Hello,
Xtend will automatically configure itself to work for most projects, but if yours requires special configuration, I would recommend checking the documentation in your project's Included Files area or online at docs.xgasoft.com/xtend
Especially make sure that the xtend.scale.view setting is set to the same viewport number as your camera is assigned to. Your camera resolution will be adopted as the base resolution, which may or may not be what you want. Consider how you want your game to scale on the lowest aspect ratio and the highest aspect ratio and set your viewport resolution accordingly.