Registering a sending number in South Korea — required before you can send

To send text messages or Alimtalk in South Korea you must register the sending number in advance. This is not a Sendgo policy — it is a legal requirement (전기통신사업법 §84-2, prohibition on caller ID spoofing).

This step is the usual bottleneck. Document review takes time, and most teams start it only after the code is written. Start it first.

Two kinds of sender key

Key	Identifies	Used by
senderKey	A registered SMS sending number	SMS · LMS · MMS, and Alimtalk SMS fallback
kakaoSenderKey	A connected KakaoTalk channel (sender profile)	Alimtalk, Brand Message

Alimtalk alone needs only kakaoSenderKey, but the moment you enable SMS fallback you also need senderKey. In practice almost everyone enables fallback, so prepare both.

Registering an SMS sending number

1. Sendgo console → Sender numbers → Register
2. Enter the number and the registered holder's details
3. Submit documentation
   • Proof of subscription showing the number belongs to the applicant
   • Business registration certificate, for a corporate holder
   • Letter of delegation, if the number is in someone else's name
4. Wait for review

Where this usually fails

• The name on the proof does not match the business details on the account. Common when registering a branch or subsidiary number under a head-office account.
• The document is old. Reissue it — recent dates are expected.
• Representative numbers (1588, 1600 and similar) may need extra line-ownership verification.

Connecting a Kakao sender profile

Alimtalk needs a KakaoTalk channel, separate from the SMS number.

1. Create a KakaoTalk channel at Kakao Business
2. Convert it to a business channel (requires business verification)
3. Sendgo console → Kakao sender profile → Register
4. Enter the channel search ID and verify via the administrator's phone
5. Store the issued kakaoSenderKey

SENDGO_KAKAO_SENDER_KEY=your_kakao_sender_key
SENDGO_SMS_SENDER_KEY=your_sms_sender_key

Where this usually fails

• A regular channel will not work. Without the business conversion you cannot create a sender profile.
• You must verify with a Kakao account that administers the channel.
• The channel search ID is the @-prefixed identifier, not the display name.

Sending before registration completes

An unregistered number fails at send time, not at signup.

Code	Cause
INVALID_KAKAO_SENDER_KEY	Sender profile key does not exist or is not owned by this account
SENDER_NOT_REGISTERED family	SMS sending number unregistered or still pending

Check the console shows approved, not "under review". Pending numbers do not send.

Registering over the API

Everything above can be done from code — including mobile numbers.

Target	API
SMS sending number (landline, representative, corporate, delegated)	POST /api/v2/senders
SMS sending number (mobile)	POST /api/v2/senders — ID document instead of PASS
Kakao channel verification code	POST /api/v2/kakao-senders/token
Kakao sender profile registration	POST /api/v2/kakao-senders

For mobile numbers the console uses PASS identity verification; over the API you attach an ID document and a Sendgo operator verifies it. Numbers filed that way are never auto-approved.

Channel registration still needs a person to read the verification SMS — but they read it on your screen. See doing everything over the API.

Next

• Send your first Kakao Alimtalk in five minutes
• Registering and getting an Alimtalk template approved