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Follow this link to see the available user types https://www.esri.com/en-us/arcgis/products/arcgis-online/buy. MobileMap requires Editor Contributor user type to enable create/edit/delete of features. Many users prefer to purchase the the Field Mobile Worker user type at the higher price so they can access other Esri applications such as Collector (soon to be replaced by Field Maps), Survey123, Dashboards, etc. The Field Mobile Worker user type is not needed, however, if you only plan to use MobileMap (and WSG InventoryManager).
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