AR is more realistic when virtual objects in your scene cast shadows onto the physical world. 8th Wall XR provides a material and a shader that can be used on transparent surfaces.
Under Assets/XR/Materials/, you will find a material called "XRTransparentSurface". Apply the material to the surface object you want to make transparent (i.e. a ground plane)
Or, create a material (for example, call it MyXRTransparentSurface), and select 8thWall -> XRShadow from the list of shaders, then apply the material to the surface object you want to make transparent (i.e. a ground plane):
To adjust the opacity of the shadows, select your Directional Light, and adjust the Strength of the shadow. To improve shadow quality, set resolution to "Very High Resolution"
For improved shadow quality, go to Edit -> Project Settings -> Quality. Set Shadow Resolution to "Very High Quality" and Shadow Projection to "Close Fit"
Also, check the "Default" quality settings (indicated by GREEN checkbox) for each platform, and make that shadows are enabled:
If needed, change the default quality level by clicking on the "down arrow" under each platform and selecting a higher quality that has appropriate shadow settings: