If the application is targeting multiple frameworks e.g. NET Core 2.1 and .NET Framework 4.6.1, you will need to install Hosting Bundle for it. Here is how;
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https://dotnet.microsoft.com/en-us/download/dotnet/2.1
Restart your IIS box.
Make sure App poll is using v4.0 of .NET CLR version.
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This will also help to solve this error;
IIS: Handler “aspNetCore” has a bad module “AspNetCoreModuleV2” in its module list
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