Authentication by SMS one-time password (OTP) unavailable for phone numbers in China

Effective immediately, SMS OTP cannot be delivered to phone numbers in China due to newly tightened local restrictions on inbound SMS traffic. As a result, Signers with Chinese phone numbers cannot use SMS OTP for authentication.

If you currently set the signature_authentication_mode to opt_sms in the Signer creation endpoint, authentication by SMS will not be possible for Chinese numbers. Please use one of the following alternatives:

• Use Email one-time password by setting signature_authentication_mode to opt_email.
• If you are using Advanced Electronic Signature (AES), consider upgrading to Qualified Electronic Signature (QES) for Chinese Signers, which does not rely on SMS OTP.

For more details, see our Authentication modes guide.