iMIS api calls failing on PUT and POST api calls with 400 errors

jQuery.ajax("https://www.test.org/iMIS/api/cs_Event_Speakers", {
type : "GET",
contentType: "application/json",
headers: {"RequestVerificationToken": document.getElementById("__RequestVerificationToken").value},
success: function(data){console.log(data);}
})
The following is failing with a 400 error however:

var apiData = {

Abstract: "test",
Agreement: 1,
Assistant_Info: 0,
Date_Modified: "01-01-2020"
Event_Code: 465,
File_Location: "C:\Path\To\File",
Function_Code: 746,
Function_End_Date: 038,
Function_Start_Date: "01-01-2020"};

 jQuery.ajax("https://www.test.org/iMIS/api/cs_Event_Speakers", {
                    type : "POST",
                    data: apiData, 
                    contentType: "application/json",
                    headers: {"RequestVerificationToken": document.getElementById("__RequestVerificationToken").value},
                    success: function(data){console.log(data);}
    })

Any help on this would be greatly appreciated!