Thanks for contacting Syncfusion support.
Anybody can download our NPM package. However, to use our package legally they needed to get license from us by visiting syncfusion.com and signing up for license. This is also mentioned in our licensing document in NPM package.
Please find its content from GitHub link
We don’t have any source level license validation, so you don’t have to do anything in your application for license validation. Our current license validation is fully based on support and new feature requests. Also, you can use the packages from the Syncfusion installed location.