I recently delved into this, Field Service for on prem. I needed to evaluate the features of field service to replace our current solution which uses Service Activities and the Service Calendar.
To install Field Service on prem you need to have a 'Dual Use Rights License'. I had to purchase one as my existing on prem licenses were not dual use. The steps to get this working:
Setup an Office365 tenant (if you don't already have one) and get whatever agreements in place between you and your Microsoft partner so that licenses/subscriptions you buy are assigned to your tenant.
Purchase an appropriate dual rights license. I purchased a 'Dynamics 365 for Field Service' license subscription. The license will appear in the tenant.
Now go through the on prem Field Service install and when the popup appears at the license validation step login to your tenant which should recognise the valid dual use license and away you go.
I found this link which helped once I'd got the dual use license in place:https://community.dynamics.com/crm/b/bringyourcode2life/posts/field-service-on-premise-6-2-1-setupRegards,Paul.
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