A license string is a string of characters developers add to their application code to license their use of applications built with ArcGIS Maps SDKs for Native Apps
A license string isn't required when developing the apps; developers can access all capabilities of the Native Maps SDK API by omitting the license string.
A license string is required to deploy an app, even when using an API keyLicensed For Developer Use Only watermark.
A free ArcGIS Runtime Lite license string is available with any ArcGIS Developer subscription