Data transfer in application/json format:
             
             1) Creation of the TextField custom field:
             
             data: {
                entityType: "contact",
                label: "Sample TextField",
                fieldType: 0,
                position: 0,
                mask: {"size":"40"}  // This is the TextField size. All other values are ignored.
             }
             
             
             2) Creation of the TextArea custom field:
             
             data: {
                entityType: "contact",
                label: "Sample TextArea",
                fieldType: 1,
                position: 1,
                mask: '{"rows":"2","cols":"30"}' // This is the TextArea size. All other values are ignored.
             }
             
             
             3) Creation of the SelectBox custom field:
             
             data: {
                entityType: "contact",
                label: "Sample SelectBox",
                fieldType: 2,
                position: 0,
                mask: ["1","2","3"]  // These are the SelectBox values.
             }
             
             
             
             4) Creation of the CheckBox custom field:
             
             data: {
                entityType: "contact",
                label: "Sample CheckBox",
                fieldType: 3,
                position: 0,
                mask: ""     
             }
             
             
             
             5) Creation of the Heading custom field:
             
             data: {
                entityType: "contact",
                label: "Sample Heading",
                fieldType: 4,
                position: 0,
                mask: "" 
             }
             
             
             
             6) Creation of the Date custom field:
             
             data: {
                entityType: "contact",
                label: "Sample Date",
                fieldType: 5,
                position: 0,
                mask: "" 
             }
             
             

application/json

{
  "status": 0,
  "response": {
    "relativeItemsCount": 0,
    "entityId": 14523423,
    "label": "Birthdate",
    "fieldValue": "2022-10-08T15:03:33.1475255Z",
    "fieldType": 5,
    "position": 10,
    "mask": "",
    "id": 0
  }
}

text/xml

<result>
  <status>0</status>
  <response>
    <relativeItemsCount>0</relativeItemsCount>
    <entityId>14523423</entityId>
    <label>Birthdate</label>
    <fieldValue>2022-10-08T15:03:33.1475255Z</fieldValue>
    <fieldType>5</fieldType>
    <position>10</position>
    <mask></mask>
    <id>0</id>
  </response>
</result>