One API

One API is a single endpoint that sends a message over whichever channel you name, and automatically retries the next channel in a chain you define when the first one fails. It replaces five request shapes, five error conventions and five sets of retry logic with one contract.

It is additive. Every dedicated endpoint under /v1/whatsapp, /v1/sms, /v1/rcs, /v1/email and /v1/instagram keeps working exactly as before, including campaigns, templates and per-channel analytics that only exist there.

Five channels are reachable through the unified endpoint. Voice uses its own endpoint because a call is not a message, but it authenticates with the same key.

POST /messages/send

Send a message over a single channel. The example below delivers a WhatsApp template with two positional variables.

curl -X POST https://slide.synquic.com/api/v1/messages/send \
  -H "Authorization: Bearer sk_live_YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "to": "+919876543210",
    "channel": "whatsapp",
    "template": {
      "name": "order_confirmation",
      "languageCode": "en",
      "variables": { "1": "John", "2": "ORD-12345" }
    }
  }'

Request body

Response

Every response carries the channel that actually delivered the message and the full ordered list of attempts, whether or not a fallback was needed.

How the chain resolves

Set fallbackChannels and One API walks the chain in order: it attempts the primary channel, and on failure moves to the next entry until one delivers or the list is exhausted. There is no orchestration code on your side and no polling. If every channel fails you get a single 502 carrying the complete attempt log.

Worked example

WhatsApp first, SMS if it does not land. The sms object holds overrides that apply only if the SMS leg is actually used.

curl -X POST https://slide.synquic.com/api/v1/messages/send \
  -H "Authorization: Bearer sk_live_YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "to": "+919876543210",
    "channel": "whatsapp",
    "fallbackChannels": ["sms"],
    "message": "Your order ORD-12345 has shipped!",
    "template": { "name": "order_shipped", "languageCode": "en" },
    "sms": { "senderId": "ACMEIN" }
  }'

Reading the attempts array

Here WhatsApp failed and SMS delivered. channelUsed is the one that worked, and every attempt is listed in the order it was made, so you can log exactly what happened without a second API call.

{
  "status": "sent",
  "channelUsed": "sms",
  "messageId": "sms_9f2a1c8e7b3d",
  "attempts": [
    {
      "channel": "whatsapp",
      "status": "failed",
      "error": "Template not delivered to this recipient"
    },
    {
      "channel": "sms",
      "status": "sent",
      "messageId": "sms_9f2a1c8e7b3d"
    }
  ]
}

One API uses the same bearer token as every other endpoint. There is nothing new to provision: a key that already carries the per-channel send scopes works immediately.

curl -X POST https://slide.synquic.com/api/v1/messages/send \
  -H "Authorization: Bearer sk_live_YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{ "to": "+919876543210", "channel": "sms", "message": "Hello" }'

Create and scope keys from API keys in the dashboard. Rate limits are shared with the dedicated endpoints rather than additional to them, see rate limits.

Standard HTTP semantics, plus one outcome specific to this endpoint: a 502 means the chain was walked in full and nothing delivered.