Result of POST /api/v3/lists/{ID}/customfields
Failed with code 400
object(stdClass)#5 (2) {
  ["Code"]=>
  int(255)
  ["Message"]=>
  string(49) "The Custom Field name already exists in this list"
}
Result of POST /api/v3/lists/{ID}/customfields
Failed with code 400
object(stdClass)#7 (2) {
  ["Code"]=>
  int(255)
  ["Message"]=>
  string(49) "The Custom Field name already exists in this list"
}
Result of POST /api/v3/lists/{ID}/customfields
Failed with code 400
object(stdClass)#6 (2) {
  ["Code"]=>
  int(255)
  ["Message"]=>
  string(49) "The Custom Field name already exists in this list"
}