Web api not supporting POST method
Change your action to be like Post([FromBody]string schooltypeName)
as by default string type is expected to come Uri.
Updated:
Change your body to just "Aided"
as currently you would need a class to make the deserialiation work otherwise (ex:class School { public string SchoolTypeName { get; set; } }
See the using namespace at the top of the controller, if you're using System.Web.Mvc, then this problem might be occurred:
Use this:
using System.Web.Http;