The FlipSend API

https://api.flipsidedigital.com.au/v1

Every request goes over HTTPS. Requests and responses are JSON.

Every request needs an API key. Create one in the FlipSend dashboard under Settings, then API keys. The key is shown once when you create it, so store it somewhere safe. Anyone holding a key can send on your account's credits.

Send it as a bearer token, or in an X-API-Key header:

Authorization: Bearer fs_live_xxxxxxxx
X-API-Key: fs_live_xxxxxxxx

Keys carry scopes. Grant only what an integration needs.

Check a key works:

curl https://api.flipsidedigital.com.au/v1/ping \
  -H "Authorization: Bearer $FLIPSEND_API_KEY"

{"ok":true,"tenant_id":"...","scopes":["messages:send","messages:read"]}

POST /v1/messages. One endpoint for all three channels, the channel field selects which. Returns 202 Accepted with a message id once the message is queued.

Set reference to your own identifier, an order number or booking id. It is stored against the message and returned in status reads, so you can reconcile against your own records.

SMS

curl -X POST https://api.flipsidedigital.com.au/v1/messages \
  -H "Authorization: Bearer $FLIPSEND_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: appt-8891" \
  -d '{
    "channel":   "sms",
    "to":        "+61400111222",
    "body":      "Your appointment is confirmed for Wed 2 July, 2:30 pm.",
    "from":      "NorthDental",
    "reference": "APPT-8891"
  }'

Email

curl -X POST https://api.flipsidedigital.com.au/v1/messages \
  -H "Authorization: Bearer $FLIPSEND_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "channel":   "email",
    "to":        "patient@example.com.au",
    "subject":   "Your statement is ready",
    "html":      "<p>Your statement is ready to view.</p>",
    "reference": "INV-10482"
  }'

One of html or text is required. Email is sent on your verified sending domain.

Fax

curl -X POST https://api.flipsidedigital.com.au/v1/messages \
  -H "Authorization: Bearer $FLIPSEND_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "channel":         "fax",
    "to":              "+61370000000",
    "document_base64": "<base64 PDF>",
    "document_name":   "referral-2211.pdf",
    "page_count":      2,
    "reference":       "REF-2211"
  }'

Fax is charged per page, so page_count is required.

Response

{
  "id":        "a495fa09-7f22-4677-b582-1be88c8c30fc",
  "channel":   "sms",
  "status":    "queued",
  "reference": "APPT-8891"
}

Send an Idempotency-Key header on any send. The first request with a given key is processed normally. Any repeat within 24 hours returns the original response instead of sending again, with an Idempotent-Replayed: true header.

Idempotency-Key: order-1024

Requires the messages:read scope. Fetch a single message by id, or list recent messages and filter by your own reference.

curl https://api.flipsidedigital.com.au/v1/messages/<id> \
  -H "Authorization: Bearer $FLIPSEND_API_KEY"

curl "https://api.flipsidedigital.com.au/v1/messages?reference=APPT-8891" \
  -H "Authorization: Bearer $FLIPSEND_API_KEY"

List accepts channel, reference and limit (default 50, maximum 200), newest first.

{
  "id":                  "a495fa09-7f22-4677-b582-1be88c8c30fc",
  "channel":             "sms",
  "status":              "sent",
  "to":                  "+61400111222",
  "reference":           "APPT-8891",
  "provider_message_id": "a9224fed-4703-4aee-b5e0-b684dc352348",
  "created_at":          "2026-07-18T10:29:29.328Z",
  "updated_at":          "2026-07-18T10:29:29.427Z"
}

FlipSend handles opt-out for you. Every SMS carries an opt-out link and every email a one-click unsubscribe, and a recipient who opts out is suppressed on your account. Sending to a suppressed recipient returns 409 rather than delivering.

Read your opt-outs with the optouts:read scope, newest first and cursor-paginated. Use this to sync on first connect and to reconcile after any webhook downtime.

curl "https://api.flipsidedigital.com.au/v1/optouts?since=2026-08-01T00:00:00Z&channel=sms&limit=200" \
  -H "Authorization: Bearer $FLIPSEND_API_KEY"

{
  "optouts": [
    {
      "event_id":    "evt_01J8...",
      "event":       "optout.created",
      "tenant_id":   "...",
      "occurred_at": "2026-08-08T04:22:11Z",
      "phone":       "+61400111222",
      "email":       null,
      "channel":     "sms",
      "source":      "link",
      "reference":   "APPT-8891",
      "message_id":  "..."
    }
  ],
  "next_cursor": "eyJ0cyI6..."
}

Pass next_cursor back as cursor to page through. since filters on occurred_at. Check a single number with GET /v1/optouts/{phone}.

Rather than polling, have opt-outs pushed to you in real time. Set an endpoint URL in the FlipSend dashboard under Webhooks. When a recipient opts out, FlipSend POSTs an optout.created event to your URL with the same body as the feed above.

POST https://your-app.example.com/webhooks/flipsend
X-FlipSend-Event: optout.created
X-FlipSend-Event-Id: evt_01J8...
X-FlipSend-Timestamp: 1786166108
X-FlipSend-Signature: sha256=<hex>

Verify the signature

Compute HMAC-SHA256 over timestamp + "." + rawBodyusing your endpoint's signing secret, and compare it to the hex in X-FlipSend-Signature. Reject any request whose X-FlipSend-Timestamp is more than five minutes old. Return 2xx to acknowledge.

60 requests per minute per key. Every response carries X-RateLimit-Limit and X-RateLimit-Remaining. Over the limit returns 429 with a Retry-After header (seconds) so you can back off precisely.

Errors return JSON with an error code and a human-readable message.

{
  "error":   "insufficient_credits",
  "message": "Not enough sms credits.",
  "required": 1,
  "available": 0
}

Email support@flipsidedigital.com.au and one of our team will help. FlipSend by Flipside Digital, Australian-built, Australian-hosted, Australian-supported.