We have introduced a new licensing system starting with version 16.2.0.x release of Essential Studio. If you reference Syncfusion assemblies from evaluation builds or from the NuGet feed, you also have to include a license key in your projects. Please note that this license key is different from the setup unlock key that you might have used in the past, and needs to be separately generated from Syncfusion website. A licensing validation message will be shown if this license key is missing. Please refer the below link for more details.