问ajax post到api控制器上的400错误

EN

function saveState() {
        const gridInstance = $("#ClaimsGrid").dxDataGrid("instance");
        var userstate = gridInstance.state();
        var data = { StateTypeID: 1, StateChange: userstate };
        $.ajax({
            type: "POST",
            data: JSON.stringify(data),
            url: "/api/PostUserState",
            contentType: "application/json",
            success: function () {
                alert("Your grid profile has been saved");
            },
            error: function () {
                alert("An error occurred during save of your grid profile");
            }
        });
    }

 public class UserStateChange
    {
        public int StateTypeID { get; set; }
        public string StateChange { get; set; }
    }

        [HttpPost("/api/PostUserState")]
        public bool PostUserState([FromBody] UserStateChange state)
        {
            var UserID = new Guid(HttpContext.Session.GetString("UserId").ToString());
            UserState mod = new UserState();

            var cur = _context.UserState.First(a => a.AppUserID == UserID && a.StateTypeID == state.StateTypeID);

            //... more logic here


            return true;
        }