Ubuntu – How to send a text message with Whatsapp Cloud API

I’m having troubles using Whatsapp Cloud API (which was released to the public on May 22). I did everything in the getting started in "Set up Developer Assets and Platform Access" section, that way I was able to send the template hello world in Ubuntu 20.04.4 LTS with:

curl -i -X POST 
https://graph.facebook.com/v14.0/my_number/messages 
-H 'Authorization: Bearer my_token' 
-H 'Content-Type: application/json' 
-d '{ "messaging_product": "whatsapp",
  "to": "my_reciever",
  "type": "template",
  "template": { "name": "hello_world", "language": { "code": "en_US" } }
  }'

or with Python 3.10 and requests 2.27.1 with:

from requests import Session
import json
from requests.exceptions import ConnectionError, Timeout, TooManyRedirects

BASE_URL = "https://graph.facebook.com/"
API_VERSION = "v13.0/"
SENDER = "my_number/"
ENDPOINT = "messages"
URL = BASE_URL + API_VERSION + SENDER + ENDPOINT
API_TOKEN = "my_token"
TO = "my_reciever"
headers = {
    "Authorization": f"Bearer {API_TOKEN}",
    "Content-Type": "application/json"
}
parameters = {
    "messaging_product": "whatsapp",
    "recipient_type": "individual",
    "to": TO,
    "type": "template",
    "template": {"name": "hello_world", "language": {"code": "en_US"}}
}
session = Session()
session.headers.update(headers)
try:
    response = session.post(URL, json=parameters)
    data = json.loads(response.text)
    print(f"data: {data}")
except (ConnectionError, Timeout, TooManyRedirects) as e:
    print(e)

Then, I tried to send a text message with this:

from requests import Session
import json
from requests.exceptions import ConnectionError, Timeout, TooManyRedirects

BASE_URL = "https://graph.facebook.com/"
API_VERSION = "v13.0/"
SENDER = "my_number/"
ENDPOINT = "messages"
URL = BASE_URL + API_VERSION + SENDER + ENDPOINT
API_TOKEN = "my_token"
TO = "my_reciever"
headers = {
    "Authorization": f"Bearer {API_TOKEN}",
    "Content-Type": "application/json"
}
parameters = {
    "messaging_product": "whatsapp",
    "recipient_type": "individual",
    "to": TO,
    "type": "text",
    "text": {
        "preview_url": "false",
        "body": "MESSAGE_CONTENT"
    }
}
session = Session()
session.headers.update(headers)
try:
    response = session.post(URL, json=parameters)
    data = json.loads(response.text)
    print(f"data: {data}")
except (ConnectionError, Timeout, TooManyRedirects) as e:
    print(e)

And, even though the response is correct, something like this:

{'messaging_product': 'whatsapp', 'contacts': [{'input': 'my_reciever', 'wa_id': 'my_reciever'}], 'messages': [{'id': 'wamid.HBgMNTchangingMDYyM0I2AA=='}]}

I don’t recieve any message in my_reciver. I don’t know what I’m doing wrong, I might have to configure the webhook for this to work? Do I need to opt-in before recieve the message (this can be read in get-started page)?

I even tried using some unofficial wrappers in python like heyoo, but I got the same result.

Hope someone can help me with this, thanks.

Note: this is a similar post, but that one is with node, not Python or Curl, so I guess this does not count as repost.