cast-ghl-plugin/GHL_API_REFERENCE.md

# GHL Conversation Provider — API Reference

**GHL API Base URL:** `https://services.leadconnectorhq.com`
**GHL Marketplace:** `https://marketplace.gohighlevel.com`
**API Version Header:** `Version: 2021-04-15`

---

## Overview

This document covers the GHL APIs used by the Cast GHL Provider bridge service. The bridge acts as a custom SMS Conversation Provider, receiving outbound webhooks from GHL and posting inbound messages + status updates back.

---

## Authentication

### OAuth 2.0

All GHL API calls require a Bearer token obtained via the OAuth 2.0 flow.

**Header:**
```
Authorization: Bearer <access_token>
Version: 2021-04-15
```

Access tokens expire after ~24 hours. Use the refresh token to obtain a new one.

---

## OAuth Endpoints

### 1. Authorization URL (user-facing redirect)

```
GET https://marketplace.gohighlevel.com/oauth/chooselocation?
  response_type=code&
  redirect_uri={REDIRECT_URI}&
  client_id={CLIENT_ID}&
  scope={SCOPES}
```

| Param | Description |
|-------|-------------|
| `response_type` | Always `code` |
| `redirect_uri` | Your OAuth callback URL (must match app config) |
| `client_id` | From GHL Marketplace app settings |
| `scope` | Space-separated list of scopes |

**Required scopes:**
```
conversations/message.write conversations/message.readonly conversations.write conversations.readonly contacts.readonly contacts.write
```

After authorization, GHL redirects to: `{redirect_uri}?code={authorization_code}`

### 2. Token Exchange

**`POST /oauth/token`**

Exchange an authorization code for access + refresh tokens.

```
Content-Type: application/x-www-form-urlencoded

client_id={CLIENT_ID}&
client_secret={CLIENT_SECRET}&
grant_type=authorization_code&
code={CODE}&
redirect_uri={REDIRECT_URI}
```

**Response — 200 OK:**
```json
{
  "access_token": "eyJhbGc...",
  "refresh_token": "def50200...",
  "expires_in": 86400,
  "token_type": "Bearer",
  "locationId": "GKAWb4yu7A4LSc0skQ6g",
  "companyId": "GK12345...",
  "userType": "Location"
}
```

### 3. Token Refresh

**`POST /oauth/token`**

```
Content-Type: application/x-www-form-urlencoded

client_id={CLIENT_ID}&
client_secret={CLIENT_SECRET}&
grant_type=refresh_token&
refresh_token={REFRESH_TOKEN}
```

**Response:** Same shape as token exchange.

---

## Webhook: ProviderOutboundMessage

GHL sends this webhook to your Delivery URL whenever a user sends an SMS from GHL (Conversations, Workflows, Bulk Actions, Mobile App).

**Method:** POST
**Signature header:** `x-wh-signature` (ECDSA P-256 + SHA-256, base64-encoded ASN.1 DER)

### Payload Schema

```json
{
  "contactId": "GKBhT6BfwY9mjzXAU3sq",
  "locationId": "GKAWb4yu7A4LSc0skQ6g",
  "messageId": "GKJxs4P5L8dWc5CFUITM",
  "type": "SMS",
  "phone": "+15864603685",
  "message": "The text message to be sent to the contact",
  "attachments": ["https://example.com/image.png"],
  "userId": "GK56r6wdJDrkUPd0xsmx"
}
```

| Field | Type | Description |
|-------|------|-------------|
| `contactId` | string | GHL contact ID |
| `locationId` | string | GHL sub-account (location) ID |
| `messageId` | string | GHL message ID — use for status updates |
| `type` | string | `"SMS"` or `"Email"` |
| `phone` | string | Recipient phone in E.164 format |
| `message` | string | Message body to send |
| `attachments` | array | URLs of attached media (MMS) |
| `userId` | string | GHL user who sent the message |

### Webhook Signature Verification

1. Read the raw request body
2. Compute SHA-256 hash of the body bytes
3. Base64-decode the `x-wh-signature` header value
4. Verify the ECDSA ASN.1 DER signature using the public key from your GHL app settings

```go
hash := sha256.Sum256(body)
sigBytes, _ := base64.StdEncoding.DecodeString(signatureHeader)
valid := ecdsa.VerifyASN1(publicKey, hash[:], sigBytes)
```

The public key is provided in PEM format in your GHL Marketplace app settings under the webhook configuration.

---

## Conversation APIs

### Update Message Status

**`PUT /conversations/messages/{messageId}/status`**

Update the delivery status of an outbound message. Only the conversation provider's own marketplace app token can update status.

**Headers:**
```
Authorization: Bearer <access_token>
Content-Type: application/json
Version: 2021-04-15
```

**Request Body:**
```json
{
  "status": "delivered"
}
```

| Status Value | Meaning |
|-------------|---------|
| `delivered` | Message delivered to recipient |
| `failed` | Message failed to send |
| `pending` | Message accepted, delivery in progress |

**Response — 200 OK:**
```json
{
  "success": true
}
```

### Add Inbound Message

**`POST /conversations/messages/inbound`**

Post an inbound (received) message into a GHL conversation.

**Headers:**
```
Authorization: Bearer <access_token>
Content-Type: application/json
Version: 2021-04-15
```

**Request Body (SMS — default provider):**
```json
{
  "type": "SMS",
  "message": "Reply from the recipient",
  "phone": "+639171234567"
}
```

| Field | Type | Required | Description |
|-------|------|----------|-------------|
| `type` | string | Yes | `"SMS"` for default provider |
| `message` | string | Yes | Inbound message body |
| `phone` | string | Yes | Sender's phone in E.164 format |
| `conversationProviderId` | string | No | Not required for default SMS provider |

**Response — 200 OK:**
```json
{
  "conversationId": "...",
  "messageId": "..."
}
```

**Note:** The `phone` number must match an existing contact in GHL. If no contact exists with that phone number, you may need to create one first via the Contacts API.

---

## Conversation Provider Setup

### Required Scopes

| Scope | Purpose |
|-------|---------|
| `conversations/message.write` | Outbound webhook events, inbound messages, status updates |
| `conversations/message.readonly` | Read message data, recordings, transcriptions |
| `conversations.write` | Create/update/delete conversations |
| `conversations.readonly` | Query conversations |
| `contacts.readonly` | Look up contacts by phone |
| `contacts.write` | Create contacts for unknown inbound numbers |

### Provider Configuration (in GHL Marketplace app)

1. Type: **SMS**
2. Name: **Cast SMS**
3. Delivery URL: `https://ghl.cast.ph/api/ghl/v1/webhook/messages`
4. Do NOT check "Is this a Custom Conversation Provider"

### Enabling the Provider (per sub-account)

After OAuth install:
1. Go to sub-account Settings → Phone Numbers → Advanced Settings
2. Select "Cast SMS" as the SMS Provider
3. Save

### Supported GHL Features

| Feature | Supported |
|---------|-----------|
| Conversations (web app) | Yes |
| Conversations (mobile app) | Yes |
| Workflows (SMS module) | Yes |
| Bulk Actions | Yes |
| Missed Call Text-Back | No (falls back to Twilio) |
| Review Requests | No (falls back to Twilio) |
| Internal SMS Notifications | No (falls back to Twilio) |
| Conversational AI | No (GHL limitation) |

---

## Rate Limits

GHL API rate limits vary by plan. The bridge should handle 429 responses gracefully:

- Retry after the `Retry-After` header value
- Max 3 retries per request
- Log rate limit events for monitoring

---

## Error Handling

GHL API errors return JSON with an error description:

```json
{
  "statusCode": 401,
  "message": "Unauthorized"
}
```

Common errors:

| Status | Cause | Action |
|--------|-------|--------|
| 401 | Token expired or invalid | Refresh token and retry |
| 403 | Insufficient scopes | Check app scope configuration |
| 404 | Message or contact not found | Log and skip |
| 422 | Invalid request body | Log and fix request format |
| 429 | Rate limited | Retry after Retry-After header |