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How to get a development license?
First lets be clear here, there is really no such thing as a "Developer License". Only Development Granules, that provides the access to the full development environment.
So the answer depends on if you are a customer or a partner.
Customer developement license:
"End User Licenses"are the ones sold to NAV customers by NAV partners.
A customer may choose to buy the Development Granules. The price depends on which granules are selected. It used to be around the price of 10-25 user CAL's. The customer is not given a separate development license, but the development granules becomes part of their regular license.
Contact your Dynamics partner to buy the development granules.
Source: Dynamics365UserGroup