Why no atmosphere in my exported project on mobile device

Hi, I am trying to export my project on my mobile device.
But I can’t understand why once I exported my project, in my mobile device it appears like in the image. And a message says “On Mobile the Sky Atmosphere component need a mesh with a material tagged as IsSky and using the SkyAtmosphere nodes to visualize the Atmosphere” I tryed to insert a mesh into the scene with the material like explained in to the massage but not works.
https://ibb.co/6b389ND
Could someone help me ?