sinch-verification-api

Original：🇺🇸 English

Translated

Verify phone numbers via SMS, Flashcall, Phone Call, Data (seamless carrier-level), or WhatsApp with Sinch Verification API. Use when implementing user phone verification, OTP, two-factor authentication, or number ownership confirmation flows.

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Sourcesinch/skills

Added on2026-03-27

NPX Install

npx skill4agent add sinch/skills sinch-verification-api

SKILL.md Content

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Sinch Verification API

Overview

The Sinch Verification API verifies phone numbers through SMS OTP, Flashcall (missed call CLI), Phone Call (spoken OTP), Data (carrier-level), and WhatsApp OTP. Used for registration, 2FA, and number ownership confirmation.

Base URL:

https://verification.api.sinch.com

URL path prefix:

/verification/v1/

Auth: Application Key + Secret (NOT project-level OAuth2 — see Authentication Guide)

Agent Instructions

Before generating code, you MUST ask the user:

Which verification method? —
```
sms
```
,
```
flashcall
```
,
```
callout
```
,
```
seamless
```
, or
```
whatsapp
```
SDK or direct HTTP? — If SDK, which language?

Do not assume defaults or skip these questions. Wait for answers before generating code.

For SDK syntax, fetch the appropriate reference:

For direct HTTP, use the API Reference (Markdown) for request/response schemas.

Getting Started

Authentication

See sinch-authentication skill for dashboard setup.

The Verification API uses Application Key + Application Secret (from your Sinch dashboard app), not project-level OAuth2. Three auth methods are supported:

Method	Use for
Application Signed Request	Secure authentication method for production traffic
Basic Auth	Simple method for prototyping and trying out API calls
Public Auth	Insecure environments (end user's device). Android/iOS SDK only, requires callback webhook

Minimum auth level is configurable in the Sinch Dashboard — requests below that level are rejected. See the Authentication Guide for signing details.

SDK Setup

Language	Package	Install
Node.js	`@sinch/sdk-core` or `@sinch/verification`	`npm install @sinch/sdk-core`
Python	`sinch`	`pip install sinch`
Java	`com.sinch.sdk:sinch-sdk-java`	Maven dependency
.NET	`Sinch`	`dotnet add package Sinch`

All SDKs initialize with

applicationKey

+

applicationSecret

(not project credentials).

Canonical Example — Start SMS Verification

bash

# Uses Basic Auth (-u) for simplicity. Use Application Signed Requests in production.
curl -X POST https://verification.api.sinch.com/verification/v1/verifications \
  -H 'Content-Type: application/json' \
  -u YOUR_APPLICATION_KEY:YOUR_APPLICATION_SECRET \
  -d '{
    "identity": { "type": "number", "endpoint": "+12025550134" },
    "method": "sms"
  }'

Response includes

id

(verification ID),

sms.template

,

sms.interceptionTimeout

, and

_links

with localized URLs for status/report actions.

Key Concepts

Verification Methods

Method	Value	Behavior
SMS	`sms`	Sends OTP via SMS. User enters code.
FlashCall	`flashcall`	Missed call — caller ID is the OTP. Auto-intercepted on Android; manual entry on iOS/JS.
Phone Call	`callout`	PSTN call dictates an OTP code. User enters the code into the app (same flow as SMS).
Data	`seamless`	Carrier-level verification via mobile data. No user interaction. Requires account manager to enable.
WhatsApp	`whatsapp`	Sends OTP via WhatsApp message. User enters code.

Core Model

Identity: Always

{ "type": "number", "endpoint": "+E164_NUMBER" }

Verification ID: Returned on start. Used to report code or query status.
Reference: Optional unique tracking string in start request. Queryable via status endpoint.
Statuses:
```
PENDING
```
|
```
SUCCESSFUL
```
|
```
FAIL
```
|
```
DENIED
```
|
```
ABORTED
```
|
```
ERROR
```
Failure reasons (most common):
```
Invalid code
```
,
```
Expired
```
,
```
Fraud
```
,
```
Blocked
```
,
```
Denied by callback
```
. Full list in the API Reference.

API Endpoints

All endpoints documented in the Verification API Reference.

Start Verification

POST /verification/v1/verifications

Set

method

to

sms

,

flashcall

,

callout

,

seamless

, or

whatsapp

. Optional fields:

```
reference
```
— unique tracking string, passed to all events
```
custom
```
— arbitrary text (max 4096 chars), passed to all events
```
Accept-Language
```
header — controls SMS language (default
```
en-US
```
)

Method-specific options (backend-originated signed requests only):

smsOptions

,

flashCallOptions

,

calloutOptions

,

whatsappOptions

. See the API Reference for full schemas.

Report Verification

Report by identity:

PUT /verification/v1/verifications/number/{endpoint}

Report by ID:

PUT /verification/v1/verifications/id/{id}

Body includes

method

and a method-specific object with the user's input:

SMS / Phone Call / WhatsApp:
```
{ "method": "sms", "sms": { "code": "1234" } }
```
(replace method name + key accordingly)
FlashCall:
```
{ "method": "flashcall", "flashCall": { "cli": "+46000000000" } }
```
— the
```
cli
```
is the full international caller ID from the incoming missed call

Get Verification Status

By ID:

GET /verification/v1/verifications/id/{id}

By method + number:

GET /verification/v1/verifications/{method}/number/{endpoint}

By reference:

GET /verification/v1/verifications/reference/{reference}

Note: The by-identity endpoint requires

{method}

in the path — it is NOT

/verifications/number/{endpoint}

.

Common Patterns

Standard Verification Flow

Start —
```
POST /verification/v1/verifications
```
with identity + method → receive verification
```
id
```
Report — User receives code/call →
```
PUT /verification/v1/verifications/id/{id}
```
with the code/CLI

Check status —

GET /verification/v1/verifications/id/{id}

→ confirm

SUCCESSFUL

If the code expires or verification fails, you cannot re-report — start a new verification.

Webhooks (Callbacks)

For production flows, configure a callback URL in the Sinch Dashboard. The API sends:

VerificationRequestEvent — fired when a verification starts. Respond with
```
action: allow
```
or
```
action: deny
```
to approve/reject.
VerificationResultEvent — fired when a verification completes (success or failure). Use for logging, analytics, or triggering downstream actions.

Callbacks are signed — verify signatures using Callback Signing.

Gotchas and Best Practices

Auth is Application Key + Secret, not OAuth2. Do not use project-level credentials.
Use Application Signed Requests in production. Application auth protects integrity of a request
Base64-decode the secret before signing. The dashboard value is base64-encoded.
FlashCall auto-intercepts on Android only. iOS/JS users must manually enter the incoming number. Android SDK is required to intercept calls.
Method availability varies by country. SMS is the most widely available.
Codes expire. Configurable via
```
smsOptions.expiry
```
. Start a new verification if expired — you cannot re-report on a completed/expired verification.
Report by ID is more precise than reporting by phone number.
Rate limit: avoid rapid re-verification of the same number. Implement backoff.
Data verification requires account manager and mobile data (not Wi-Fi).
SMS language may be overridden by carrier compliance (e.g., US shortcode requirements).