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

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

Korean law requires the caller ID to be pre-registered. How to register an SMS sending number and connect a Kakao channel, and where registrations usually get rejected.

마크다운 원문 보기

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.

Next

자주 묻는 질문

Can I test without registering a sending number?
No. Pre-registration is a legal requirement under the Telecommunications Business Act and applies to test sends too. An unregistered number fails at send time.
Can I register a mobile number?
Yes, if it is in your own name. The registered holder must match the account; using someone else's number requires a letter of delegation.
What is the difference between kakaoSenderKey and senderKey?
kakaoSenderKey identifies a KakaoTalk channel and is used for Alimtalk and Brand Message. senderKey identifies an SMS sending number and is used for SMS/LMS/MMS and for Alimtalk SMS fallback. Enabling fallback means you need both.
How long does registration take?
It is not instant — documents are reviewed, which takes business days. Start it before you write code; it is the longest lead time in the integration.

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