Look at the name of the project that is causing the error. If you determine that the Extension SDK being referenced by your app is not supported, then you need to perform the following steps: Please check the Extension SDK vendor site to find out whether it can be referenced by UWP apps. Visual Basic, C#, C++ and JavaScript Universal Windows Platform (UWP) apps can reference Extension SDKs that target Windows 8.1, as long as these Extension SDKs do not use APIs that have been deprecated in Windows 10 and later.
REFERENCE MANAGER 12 UPGRADE UPGRADE
If you choose to retarget Windows 8.1 projects to Windows 10 and later, see Port, migrate, and upgrade Visual Studio projects. For more information, see Move from Windows Runtime 8 to UWP. Universal Windows Platform (UWP) projects can create references to other UWP projects in the solution, or to Windows 8.1 projects or binaries, provided that these projects do not use APIs that have been deprecated in Windows 10 and later. Other assemblies or class libraries of projects in the same solution You can add a reference to the following types of components and services: For more information, see How to: Add or remove references.
You can also right-click on the project node and select Add > Reference. To add a reference, right click on the References or Dependencies node in Solution Explorer and choose Add Reference. A reference is essentially an entry in a project file that contains the information that Visual Studio needs to locate the component or the service. Before you write code against an external component or connected service, your project must first contain a reference to it.