curl --request GET \
  --url https://api.multchats.com/v2/inbox/get-custom-fields-from-chat \
  --header 'Authorization: Bearer <token>'

{
  "success": true,
  "response": {
    "customFields": {
      "fields": [
        {
          "id": "<string>",
          "key": "<string>",
          "label": "<string>",
          "optionsJson": {},
          "isRequired": true,
          "sortOrder": "<string>",
          "value": "<unknown>"
        }
      ],
      "assignedTemplateIds": [
        "<string>"
      ]
    }
  }
}