The Insta360 One X2 has a setting which is missing from other Insta360 cameras: while in video recording or streaming mode, the field of view (FoV) can be changed from 360° to 150°. For use with Avatour, the 360° FoV must be selected. (The Avatour app itself allows control over the FoV.)
When in video recording or streaming mode, touch the screen once to bring up the video mode menu items. In the below picture, the incorrect setting of 150° is seen:
If this icon is showing, touch the 150° symbol to change the mode to 360°. You should see the symbol that looks like this:
Your One X2 camera is now ready to use with Avatour.