Symptoms

Unable to activate hosting or change a service plan for a subscription. It throws the below error:

Error: Service node is unknown for sysuser with id=0

Cause

A subscription has "0" resources assigned.

Resolution

If subscription is Custom (not associated with a service plan), modify subscription resources in Subscriptions > example.com > Customize

If subscription is assigned to a service plan, sync it with a service plan so that resources get updated.