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API Integration GuideWorkflow + HTTP Request

Send SMS and supported iMessage messages from GoHighLevel

GoHighLevel (HighLevel) is the all-in-one CRM and marketing platform most agencies run their clients on — sub-accounts, Workflows, pipelines, and campaigns under one roof.

SendiMessage connects through the GHL Workflow "Webhook" action: when a contact is created, a pipeline stage moves, or a campaign step fires, the action POSTs to the SendiMessage API and the message goes out on a managed line. For agencies, the strong pattern is a dedicated managed line per client sub-account, so each client's messaging is isolated, and one middleware endpoint routes SendiMessage receive events back into the right sub-account. Store the message_handle returned at send time on the GHL contact so delivery and reply events can be matched back.

Connect SendiMessage to GoHighLevel using the SendiMessage REST API, CRM workflow automation, server-side functions, or webhooks. There is no native GoHighLevel marketplace application today — the methods below are what actually works, labeled honestly.

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What this integration enables

New lead outreach
A contact enters a sub-account and the workflow's Webhook action sends the first message on that client's line.
Pipeline stage follow-up
Moving a deal stage fires a follow-up message with the contact's details merged in.
Appointment reminders
Calendar bookings trigger reminders before the appointment.
Per-client managed lines
Each agency client gets its own dedicated line, so sending and replies stay isolated per sub-account.
Two-way replies
Customer replies arrive as receive webhooks; middleware writes them back to the correct sub-account contact.
Missed-call text-back
A GHL trigger on a missed call fires a text follow-up through the API.

Implementation options

GoHighLevel Workflows (Webhook action) + HTTP request
Use GoHighLevel Workflows (Webhook action) to call POST /send-message directly when a record changes. Fastest path when your plan supports outbound HTTP calls.
Middleware integration
A small backend service sits between GoHighLevel and SendiMessage: it receives CRM events, applies your consent and formatting rules, sends the message, and writes delivery events back to the record.
Automation platform
Zapier, Make, n8n, or Power Automate can bridge GoHighLevel triggers to SendiMessage HTTP actions without custom code.
Webhook-based synchronization
SendiMessage posts outbound and receive events to your endpoint; correlate them with the stored message_handle (or ids embedded in your status_callback URL) to update the GoHighLevel timeline.

Architecture

How it fits together: GoHighLevel event, then Workflow or backend, then SendiMessage API, then Managed messaging line, then SMS or supported iMessage, then Customer, then Delivery or reply event, then Signed webhook, then GoHighLevel timeline update.
  1. GoHighLevel eventA record changes, a stage moves, or a workflow fires
  2. Workflow or backendGoHighLevel automation or your middleware prepares the request
  3. SendiMessage APIPOST /send-message — the message is validated and queued
  4. Managed messaging lineYour dedicated line sends the message
  5. SMS or supported iMessageChannel routing picks iMessage where supported, SMS otherwise
  6. CustomerThe message arrives; the customer can reply
  7. Delivery or reply eventSendiMessage records what actually happened
  8. Signed webhookYour endpoint receives outbound or receive
  9. GoHighLevel timeline updateYour handler writes the event back as activity

Example request

Workflow payload
{
  "number": "{{contact.phone}}",
  "content": "Hi {{contact.first_name}}, your appointment is tomorrow at 10:00 AM."
}

Template variables like {{contact.phone}} are illustrative — replace them with your platform's own merge syntax or values resolved by your middleware. Correlate delivery events by storing the returned message_handle on your own record.

Delivery events and incoming replies

Correlate delivery events with the message_handle you stored at send time (or with ids embedded in your per-message status_callback URL); replies carry the contact's number and conversation, which your middleware maps to the right GoHighLevel record. Automatic GoHighLevel synchronization is not built in — your handler (or automation platform) performs the write-back.

webhook event
// "outbound" event → your gohighlevel endpoint
// Verify the X-SMSBridge-Signature header (HMAC-SHA256 of the raw body
// with your webhook secret), then use GET /v2/messages/{message_handle}
// for authoritative state and match it to your contact_id in gohighlevel.

Limitations and honest notes

  • iMessage delivery is available on supported messaging lines and destinations. Recipients without iMessage receive SMS when fallback is configured — never assume universal iMessage availability.
  • Messages are accepted asynchronously — the API returns status QUEUED and final status arrives via webhook or the message endpoints.
  • No official SDK for this ecosystem yet — the example uses plain HTTP against the REST API. Official SDKs are published for JavaScript/TypeScript (npm: sendimessage), Python (PyPI: sendimessage), PHP (Composer: sendimessage/sdk), and Go (github.com/sendimessage/sendimessage-go). Every SDK is dependency-free and covers the full public API surface.
  • A native GoHighLevel marketplace application is not available today. The integration methods on this page are API-based.
  • Send messages only to recipients who expect them. Transactional and operational messaging is the primary use case — unsolicited bulk marketing is not.

Security considerations

  • Store the SendiMessage API key in GoHighLevel's credential store, your middleware's secret manager, or your automation platform's connection vault — never in front-end scripts or record fields.
  • Verify the signature header on every webhook before writing anything back to the CRM.
  • Send only the fields the message needs (phone, first name); keep full CRM records out of message payloads and logs.

Frequently asked questions

Does SendiMessage have a native GoHighLevel application?
Not today. GoHighLevel connects through the SendiMessage REST API — via GoHighLevel Workflows (Webhook action), middleware, or an automation platform. This page is an API integration guide, and statuses on this site only say "native" when a native app has actually shipped.
Can GoHighLevel workflows send SMS through SendiMessage?
Yes — any GoHighLevel automation that can make an outbound HTTP request (directly or via middleware) can call POST /send-message. The response confirms the message is queued; delivery status follows on your webhook.
Can GoHighLevel trigger iMessage?
Delivery uses iMessage on supported messaging lines and destinations, with SMS fallback when configured. Not every contact supports iMessage, so treat it as an upgrade, not a guarantee.
Can customer replies return to the CRM?
Yes. Incoming replies arrive as receive webhook events carrying the contact's number and conversation. Your middleware or automation platform matches that to the GoHighLevel record and creates timeline activity or a task.
Do I need middleware?
Only if GoHighLevel Workflows (Webhook action) can't make the HTTP calls you need, or you want central consent logic and retry handling. Many teams start with workflow + HTTP or an automation platform and add middleware as volume grows.
Where should API credentials be stored?
Server-side only: the CRM's credential store, your middleware's secrets manager, or the automation platform's connection vault. Never in client-side scripts, record fields, or shared documents.
How is pricing calculated?
Per active messaging line, billed monthly, with usage according to your agreement. The team confirms per-line pricing for your countries and volume during onboarding.
Is there a native GoHighLevel marketplace app?
No. SendiMessage does not publish a HighLevel marketplace app today. The integration uses the standard Workflow Webhook action outbound and a middleware endpoint for inbound replies — both work on standard GHL plans that allow the Webhook action.
Can each agency client have its own line?
Yes. Provision a dedicated managed line per sub-account. Send from that line by passing its line_handle, and route inbound receive events back to the matching sub-account in your middleware.

Ready to connect GoHighLevel?

Request a messaging line and a SendiMessage integration specialist will review your GoHighLevel workflow and guide the setup.