Connect 23 Telecom to Klaviyo

Setup type	Webhook · guided activation
Setup time	About 15 minutes
Sends SMS	Yes
Delivery status in Klaviyo	No — check 23 Telecom
Who can configure	Klaviyo Manager, Admin or Owner (2FA required)

Status: Managed activation

23 Telecom supports Klaviyo Flow webhooks through guided activation. Start with the sandbox recipe below; when you’re ready to launch, your account manager confirms the Flow’s stable per-event idempotency value and enables the retry-safe production path. Verify the one-off sandbox test in 23 Telecom List messages, because Klaviyo records the transport status rather than the response body.

What this connection does

A Klaviyo Webhook action inside a Flow calls the 23 Telecom API to send an SMS. Klaviyo records the HTTP status; carrier delivery reports stay in 23 Telecom.

Before you start

• A Manager, Admin or Owner role with two-factor authentication enabled (Klaviyo requires it for webhooks).
• An active workspace, an approved sender ID and an E.164 test number, e.g. +447911123456.
• A restricted 23 Telecom API key with only sms.send — start with a sandbox sk_test_ key (Sandbox & test mode).

POST  /api/v1/sms/send-individual  · Permission: sms.send

Connect 23 Telecom

1. Open your Flow, drag in a Webhook action.

2. Set the Destination URL to https://restlink23telecom.com/api/v1/sms/send-individual (HTTPS only — no self-signed certificate and no redirects).

3. Under Add Headers, add Content-Type: application/json, your secret X-API-Key, and Idempotency-Key: klaviyo-sandbox-001 for this one-off sandbox test. Do not reuse that value for another message. The production idempotency mapping is confirmed during managed activation.

4. Add the JSON Body, then Save.

Request body

Body

{
  "messages": [
    { "to": "+447911123456", "message": "Your message", "sender_id": "YourBrand" }
  ]
}

Map to and message to your profile/event variables.

Field mapping

Klaviyo field	Value
Method	POST
Destination URL	https://restlink23telecom.com/api/v1/sms/send-individual
Content-Type	application/json
X-API-Key	your restricted 23 Telecom key (sandbox first)
Idempotency-Key	one-off value for sandbox; production mapping supplied during managed activation
messages[0].to	recipient phone (E.164)
messages[0].message	your message content
messages[0].sender_id	your approved sender ID

Send a test

Use a separate test Flow or test profile with your sk_test_ key. The Webhook card → View All Activity shows the transport status, but Klaviyo does not expose the response body. After the test, find the request by phone number and time in 23 Telecom List messages, then confirm that the sandbox message exists with the expected recipient and a non-empty client_message_id.

A 2xx is not acceptance — verify in 23 Telecom

Klaviyo records the HTTP status but cannot inspect the response body. A 200 can still carry blocked_country, while missing local pricing may be accepted fail-open with a provisional local cost. For the one-off sandbox test, verify that the message appears in 23 Telecom with a generated client_message_id; never treat Klaviyo’s successful transport status alone as acceptance or use it as a reason to auto-retry.

Idempotency & retries

Klaviyo treats 2xx as success and retries 429/500/502/503 — up to 17 attempts over 24 hours. To avoid duplicate SMS you need a unique per-event value that is stable across every attempt. Dynamic-header support can vary by Flow configuration, so production activation includes a short idempotency design check with 23 Telecom. We confirm that the Flow can supply the stable value in Idempotency-Key to the strict integration endpoint; if it cannot, we scope an adapter that validates the response before launch. Keep idempotency in the request header; do not move it into the body. Do not confuse the Flow Webhook action with Klaviyo’s separate, gated Custom Action product.

Production activation

Klaviyo live traffic uses managed activation because Flow webhooks route on the transport status and production retries need a stable per-event idempotency header. Your 23 Telecom team confirms the strict integration endpoint with that header, or an adapter that validates the response body, before enabling the workspace.

When the retry-safe route is confirmed, the activation package includes the approved production URL or adapter mapping, the restricted key and a one-message launch check. Apply that configuration — rather than changing only the API key on the sandbox batch template — and then publish the Flow.

Verify the result

Accepted means queued. Read carrier delivery in Message status or Statistics, or add a live delivery webhook.

Troubleshooting

Response	Cause & fix
400 IDEMPOTENCY_KEY_REQUIRED	Add a stable per-event Idempotency-Key header; if the Flow cannot provide one, contact 23 Telecom for managed activation
401 INVALID_API_KEY	Wrong or disabled key in the secret header
403 NO_SMS_ACCESS	SMS not enabled — contact 23 Telecom
429 RATE_LIMIT_EXCEEDED	Sending faster than your budget — slow the Flow

Need help?

• Flow, webhook, roles or 2FA — Klaviyo support.
• API key, sender ID, accepted-but-not-delivered — your 23 Telecom account manager, or the contact form.

Official platform documentation

• Add a webhook action to a flow
• Understanding webhook status codes

Last verified: 16 July 2026.