Build failure due to "namespace cannot be found" error

When you are writing or using code with namespaces and assembly definitions, Unity may fail to build due to a compiler error in the following form:

The type or namespace name '<<someNamespace>>' could not be found

If this occurs, then you will need to create/edit the Assembly Definition file in the Project window folder where the scripts are located. If an Assembly Definition already exists, select it (otherwise, create a new one and select that). Then, in the Inspector window, check the Android option and click Apply:

Figure 15.28 – Adding the Android platform to the WebXR settings