WhatsApp Business messaging is available through the Sinch Conversation API. Send text, media, template, and interactive messages using the unified API format. WhatsApp has strict rules around messaging windows and template approval.

Prerequisites

A provisioned WhatsApp Business sender (via Sinch Build Dashboard or Provisioning API).
Meta-approved WhatsApp templates for outbound messaging outside the 24-hour window.
A Conversation API app in the correct region.

SDK Reference

24-Hour Customer Service Window

A user sending a message to your business opens a 24-hour window.
Each new user message resets the 24-hour timer.
Within the window: send freeform messages (text, media, interactive).
Outside the window: must use an approved template message.
Freeform messages outside the window always fail, even with opt-in.

Template Messages

Templates are pre-approved message formats registered with Meta. Required for:

First outbound contact (no open window)
Re-engaging after 24-hour window closes
Marketing, utility, and authentication use cases

template_id is the template name, not the numeric identifier. See WhatsApp Template Support and references/templates.md for structure and examples.

Template components: header (text, media, document), body, footer, buttons (quick reply, CTA, copy code), interactive elements. Each component may use placeholders fulfilled via parameters.

Template Approval Process

Create templates via Sinch Build Dashboard or Provisioning API.
Templates are submitted to Meta for review.
Meta approves or rejects (typically within 24 hours).
Categories: MARKETING, UTILITY, AUTHENTICATION.

Opt-In Requirements

All marketing, utility, and authentication conversations require user opt-in.
Opt-in can be collected via any channel (SMS, web form, email, in-app).
Permanent opt-in allows sending templates outside the window.
Opt-in does NOT allow freeform messages outside the window.

Message Types

Type	Inside Window	Outside Window
Text	Yes	No
Media (image, video, document, audio)	Yes	No
Interactive (buttons, lists)	Yes	No
Location	Yes	No
Sticker	Yes	No
Template	Yes	Yes

Media Specifications

Media Type	Formats	Max Size
Image	JPEG, PNG	5 MB
Video	MP4 (H.264 + AAC)	16 MB
Audio	AAC, MP4, AMR, MPEG, OGG (opus)	16 MB
Document	Any valid MIME type	100 MB
Sticker	WebP	100 KB

Message Examples

Send WhatsApp text / Fallback patterns — See Messages API Reference. Set channel to WHATSAPP. For fallback, add channel_priority_order and include SMS_SENDER in channel_properties.
WhatsApp message support details — See WhatsApp Message Support.

WhatsApp Gotchas

Customer Service Window is strict. Freeform messages outside 24h always fail. Use templates.
Template name vs ID. template_id expects the template name, not numeric ID.
Template rejection. Meta may reject for vague content, promotional language in utility templates, or policy violations.
Per-message pricing. Marketing and authentication templates charged on delivery. Utility templates free within session.
Rate limits. Enforced by WhatsApp based on quality rating and tier. New numbers start at 1K messages/day.
Quality rating matters. User reports/blocks lower your rating, reducing sending limits. Monitor in Meta Business Manager.
Opt-in is mandatory. Sending without opt-in risks account suspension.
Media URLs must be publicly accessible. URLs behind auth or firewalls fail.
Template parameters are positional. Indexed by position, not name. Ensure order matches definition.