How do I license Autopilot pre-provisioning foouser and autopilot user for my Intune MDM service?

If you use pre-provisioning with Intune Autopilot, Microsoft may use one or more fake pre-provision accounts which may need to be licensed for your Intune if you use UPN licensing. This user is typically foouser@your-mail-domain and may not be the same as the UPN you are trying to get licensed for.

You can see this string by investigating hklm\system\currentcontrolset\control\clouddomainjoin\joininfo\<some alphanumeric key>.

An example, taken from FooUser@ meets the Cosmic Autopilot@ user, can be seen here.