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 and to unlock certain capabilities on the deployment device.
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 key. API keys provide access to content and services, whereas a license string enables SDK capabilities and removes the Licensed For Developer Use Only watermark.
A free ArcGIS Runtime Lite license string is available with any ArcGIS Developer subscription which can be used to license an unlimited number of applications. Refer to APIs and SDKs for the target product to obtain a Runtime Lite license string (you must be logged in), or contact Esri Customer Service or the local distributor to obtain deployment packs for license levels Basic, Standard, or Advanced.