Rest API POST method getting 400 Bad request

Question

Im new on SharePoint 2016 and i want "POST" items to list `

var data = JSON.stringify($scope.formData);  
console.log(data)
data = data.replace(/[{}]/g, '');  
var datavalue = "{__metadata:{'type':'SP.Data.Task_x0020_ScheduleListItem'}," + data + "}";  
$http({  
    url:"_api/web/lists/GetByTitle('Task%20Schedule')/items", 
   //url is working fine , I just took out complete url and placed end point here 
    method: "POST",  
    headers: {  
        "Accept": "application/json;odata=verbose",  
        "Content-Type": "application/json;odata=verbose",  
        "X-RequestDigest":digestValue,
        "X-HTTP-Method": "POST"  
    },  
    data: datavalue 
}).then(function(response) {  
    digestValue=" ";
    alert("success");  
}, function(response) {  
    alert("failed");  
});

could anyone please check what is wrong with this ? i have added digest value also but when I make post call i get this error

error: {code: "-1, Microsoft.SharePoint.Client.InvalidClientQueryException", message: {lang: "en-US",…}}
code: "-1, Microsoft.SharePoint.Client.InvalidClientQueryException"
message: {lang: "en-US",…}
lang: "en-US"
value: "A 'PrimitiveValue' node with non-null value was found when trying to read the value of a navigation property; however, a 'StartArray' node, a 'StartObject' node, or a 'PrimitiveValue' node with null value was expected."

data that i am passing :

{__metadata:{'type':'SP.Data.Task_x0020_ScheduleListItem'},"Task_x0020_Type":"Reporting","Country":"America","Title":"a","Schedule_x0020_Type":"Monthly","Monthly_x0020_Type":"Day","Assignee":"results":["Title":"Lye, Nicholas"],"Escalation_x0020_Point":"results":["Title":"Lye, Nicholas"],"Due_x0020_Hour":"? undefined:undefined ?","Due_x0020_Min":"? undefined:undefined ?","Relevant_x0020_Documents":"ff###@http;://vv$$$","Monthly_x0020_Value":"30"}

Answer 1

For multiple user filed, the JSON should be similar as

var itemProperties = {
    '__metadata' : { 'type':'SP.Data.Task_x0020_ScheduleListItem' },
    'Title': 'a',
    'AssigneeId' : { 'results': [user1id,user2id] }
}

Answer 2

The value of metadata should be the list name.

Example: If your list name is Employee then the type field should be EmployeeListItem.

 var item = {
       "__metadata": { "type": "SP.Data.EmployeeListItem"  },
       "Title": "MISS",
       "FirstName": "Rudrani",
       "LastName": "Patil"                   

 },