Symptoms
Office 365 provisioning task fails:
500 Internal Server Error
[ApplicationUnknownError] Provisioning: resource 6f2cdee0-...-7d56785ee797 of type 'tenants' (http://www.parallels.com/Office365/Tenant/1.1) for APS application 'Office 365-16.5-64':
Addon with no preceding base in this order. Format should be Base, addon, addon, base, addon...or it should be addon for for existing base or addon for preceding conversion/transition item.
Cause
One of the subscription resources is an Addon without a valid parent Offer.
Resolution
Check all Addon resources intended for provisioning and make sure parent Offers are added correctly.