Overview

The Transactional API — also known internally as the SMS API — is Instasent's core SMS surface. It connects your application directly to carrier networks, delivering to handsets in 200+ countries, and covers everything you need around raw SMS: sending (single or batched), receiving DLRs and inbound, querying message history, running HLR lookups and reading price profiles and account balance.

It is the evolution of the Legacy API — same endpoint surface, modernised with DLR webhooks, per-project tokens, SMPP and the api_sms token model. If you are about to write new code, write it against this API.

Two transports expose the same underlying pipeline. Pick the one that fits your stack — most teams start with HTTP and only move to SMPP when volume or session-state requirements justify it.

What you can do

• Send SMS, one at a time — POST /sms for triggered traffic (OTPs, alerts, receipts, notifications).
• Send SMS in bulk — POST /sms/bulk takes a collection of messages in a single request. This is the endpoint for API-driven campaigns, marketing fan-outs and any high-volume dispatch. Customers including marketing agencies run entire campaigns on top of it.
• Receive delivery reports (DLRs) as carriers report status back through the chain, pushed to your webhook in real time.
• Accept inbound messages when the account has two-way enabled.
• Query message history and per-message status — GET /sms, GET /sms/{id}.
• Run HLR / number lookups — POST /lookup, GET /lookup/{id} and GET /lookup to check handset presence and routing before sending.
• Read account balance — GET /organization/account.
• Read price profiles — GET /sms/price-profile/me/countries and GET /lookup/price-profile/me/countries for per-country pricing.

When to use this API

Reach for Transactional whenever you need raw SMS capacity — single, batched, or wholesale — without asking Instasent to manage the recipient audience. Typical workloads:

• User-triggered messages — OTPs, password resets, receipts, shipping notifications. One message per event, delivered in seconds, via POST /sms.
• API-driven campaigns and bulk dispatch — marketing sends, notification fan-outs, anything that fires many messages in one go. Use POST /sms/bulk.
• SMS wholesale — aggregators, messaging platforms and resellers pushing their own traffic through Instasent. Use HTTP at moderate rates; use SMPP for carrier-grade throughput with persistent sessions.
• Pre-send validation and pricing — HLR lookup and price profiles to route and cost-check before dispatch.

If you need Instasent to own the audience, personalization, segmentation and attribution, use the Product API instead — it delegates delivery to this one but adds the customer-data layer on top. The Transactional API is the right pick when the caller already manages its recipient list and just needs the full SMS pipe.

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