WhatsApp Cloud API: Test Number Not Active After Generation

Question

I am working on WhatsApp integration using the WhatsApp Cloud API. I successfully generated a test number after completing the WhatsApp Business Login process. However, when I try to send a message using this test number through the API, I receive the following error:

{"error": {"message": "The account is not registered","type": "OAuthException","code": 133010,"error_subcode": 2593006,"is_transient": false,"error_user_title": "Account does not exist","error_user_msg": "Account does not exist in Cloud API. Please use/register API to create an account first.","fbtrace_id": "Avju9R0h5nI7P8EYGmhLtMe"}}

What I Have Done So Far:

1. Generated a test number successfully using the WhatsApp Cloud API.
2. Verified that I have the required permissions (whatsapp_business_messaging, whatsapp_business_management).
3. Checked my access token to ensure it's valid.
4. Attempted to send a message from the test number using the /messages endpoint.

Steps I Followed:

1. Generated a test number via Meta Developer Console.

2. Checked the test number in the Meta Business Manager under WhatsApp settings.

3. Verified API permissions (whatsapp_business_messaging, whatsapp_business_management).

4. Attempted to send a message using the following API request:

Code Example (API Request to Send Message)

curl -X POST "https://graph.facebook.com/v18.0/YOUR_PHONE_NUMBER_ID/messages" \
-H "Authorization: Bearer YOUR_ACCESS_TOKEN" \
-H "Content-Type: application/json" \
-d '{
      "messaging_product": "whatsapp",
      "to": "RECIPIENT_PHONE_NUMBER",
      "type": "text",
      "text": {
         "body": "Hello, this is a test message from WhatsApp Cloud API!"
      }
    }'

👉 Expected Output: The message should be sent successfully.
❌ Actual Output: The "Account does not exist" error.

Questions:

1. How do I activate the test number so it can send and receive messages?

2. Do I need to manually register the test number before using it with the Cloud API?

3. What additional steps are required after generating a test number for successful message delivery?

4. Are there any settings in the Meta Business Manager that need to be enabled for the test number to work?