EntityFramework.Functions | Functions library implements Entity Framework code | Reflection library

Looks like you are using EntityFramework.Functions package. Then take a look at Function topic. You are using Scalar-valued function, non-composable, which according to the package author

can be called directly just like other above methods

but

However, since it is specified to be non-composable, it cannot be translated by Entity Framework in LINQ to Entities queries

and

This is by design of Entity Framework

While what you need is Scalar-valued function, composable, which

works in LINQ to Entities queries, but cannot be called directly

Shortly, since you are using it inside LINQ to Entities query, use FunctionType.ComposableScalarValuedFunction inside Function annotation. And since it's not directly invokable, it doesn't need method body, so you can simply throw exception:

Well i follow this approach:

WebApiConfig.cs