curl --request POST \
  --url https://api.sendx.io/api/v1/rest/customfield \
  --header 'Content-Type: application/json' \
  --header 'X-Team-ApiKey: <api-key>' \
  --data '{
  "name": "Custom Field Example",
  "type": 0,
  "shown": true,
  "isShareable": false,
  "description": "An example custom field"
}'

{
  "id": "encrypted-id-123",
  "name": "Custom Field Example",
  "type": 0,
  "description": "An example custom field"
}