GET :http://www.Example.com/Api/1/0/Book/Company/0
[Route(\"{UserId}/{Category}/books/{BookType}/{Page}\")]
[HttpGet]
[RequestAuthorization]
add [FromUri] and try again as below
[Route("{UserId}/{Category}/books/{BookType}/{Page}")]
[HttpGet]
[RequestAuthorization]
public Response Get(([FromUri] BookbRequestModel book )
{
var books= this.contentService.GetUserItems(book.UserId,book.Category,book.BookType,book.Page)
return new Response() { Status = ApiStatusCode.Ok, Books = books};
}
for more information :-
http://www.c-sharpcorner.com/UploadFile/2b481f/parameter-binding-in-Asp-Net-web-api/