curl --request POST \
  --url https://api.getoutbox.ai/agent/chat/{agent_id} \
  --header 'Authorization: <api-key>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "message": "<string>",
  "thread_id": "<string>",
  "contact_id": "<string>",
  "phone_number": "<string>",
  "full_name": "<string>",
  "platform": "<string>",
  "external_customer_id": "<string>"
}
'

{
  "response": "<string>",
  "thread_id": "<string>",
  "thread_message_id": "<string>"
}