When you download and install the Windows Phone 8.1 SDK and run Visual Studio for the first time , you will be prompted to get a developer license . This lets you to develop and test the Windows Store app or Windows Phone store app on Windows 8.1 system before submitting it to the store for certification. You just need a Windows Live ID for this.
There are other ways in which you can let the developers to view , register or View the Developer License.
1. Use the Menu Project -> Store -> Acquire Developer License to show the register developer license dialog.
2. Use the below PowerShell commands .
This will get the information about a developer license for the current system.
This PowerShell command removes the developer license from the current system. You will be prompted to confirm that you want to remove your developer license from this computer . Enter “Y” to confirm or “N” to cancel this operation.
This PowerShell command allow the user to register a developer license.