Send reliable WhatsApp template messages

You are integrating the Akked WhatsApp API.

Base URL: https://akked.app
Authentication: Authorization: Bearer ak_live_YOUR_KEY
Requirement: an active Meta WhatsApp sender bound to the API key.
Rate limits: 60 authenticated send requests per API key per minute and 120 per sender per minute.
Billing: legacy message-credit billing reserves one account credit per message. With contact billing, the first outbound message to a contact in a billing month reserves one unit from the plan's monthly unique-contact allowance; further sends to that contact in the same month, from any of your numbers, use no additional unit. The response's credits_remaining equals the remaining unique-contact allowance; billing.contact_allowance has the full usage detail.
WhatsApp policy: use approved templates as required by Meta, respect customer consent and opt-outs, and follow the template category and messaging rules.

Workflow:
1. GET /api/v1/senders to confirm the sender bound to the API key.
2. GET /api/v1/templates to read template contracts for that sender.
3. POST /api/v1/messages with a unique Idempotency-Key header.
4. Poll GET /api/v1/messages/{id} using the returned status_url.

POST /api/v1/messages body:
{
  "to": "+E164_PHONE",
  "template_key": "one of the contracts below",
  "language": "en or ar",
  "parameters": { "exact keys required by that template": "values" }
}

Never retry with a new Idempotency-Key when the outcome is uncertain. Reuse the same key and payload. A reused key with a different payload returns 409.

Template contracts:
- order_confirmation [en, ar]: customer_name (string, required, max 120); order_number (string, required, max 80); store_name (string, required, max 120); total (string, required, max 40); currency (string, required, max 3); items (string, required, max 2000); address (string, required, max 512); order_date (string, required, max 64)
- confirmed_reply [en, ar]: customer_name (string, required, max 120); order_number (string, required, max 80)
- cancelled_reply [en, ar]: customer_name (string, required, max 120); order_number (string, required, max 80)
- paid_order [en, ar]: customer_name (string, required, max 120); order_number (string, required, max 80); store_name (string, required, max 120); total (string, required, max 40); currency (string, required, max 3); items (string, required, max 2000); address (string, required, max 512); order_date (string, required, max 64)
- abandoned_cart [en, ar]: customer_name (string, required, max 120); store_name (string, required, max 120); total (string, required, max 40); currency (string, required, max 3); cart_step (string, required, max 120); recovery_url (string, required, max 2048)
- otp [en, ar]: code (string, required, max 10)

Important errors: 401 invalid key; 402 insufficient credits or contact allowance; 403 API access or sender unavailable; 404 sender/template/message not found; 409 idempotency conflict; 422 invalid payload, template parameters, or recipient policy; 429 rate limit; 503 API queue unavailable.

Generate production code that validates configuration, preserves the Idempotency-Key across retries, logs the x-request-id response header, and never logs the API secret.