System.Threading.Tasks.Task Method Not Found

Ensure that you are using Entity Framework version 6.2

I had the same issue because I was using the Linq method FirstOrDefaultAsync() with a version of EntityFramework 6.1.3 (before 6.2.0)

According to Microsoft documentation on "QueryableExtensions.FirstOrDefaultAsync()" : https://docs.microsoft.com/en-us/dotnet/api/system.data.entity.queryableextensions.firstordefaultasync?view=entity-framework-6.2.0

This method is only available with the version of ** EntityFramework 6.2 **

Applies to

Entity Framework

6.2.0