## Choose which parties require SMS authentication

You can now set SMS one-time password (OTP) authentication for individual parties. Previously, this was an envelope-level setting: either all signers required an OTP, or none did.

This gives you more flexibility to require additional verification for selected signers within the same envelope.

### What changes in the API?

When creating an envelope:

- Include `party_mobile` for a party to require SMS OTP authentication when they sign.
- Omit `party_mobile` for a party if they do not require SMS OTP authentication.


The `envelope_requires_otp` field is still accepted but is ignored. You do not need to remove it from existing requests, but each party’s `party_mobile` now determines whether they require OTP authentication.

In responses, `envelope_requires_otp` is `true` if at least one signer on the envelope requires OTP authentication, and `false` otherwise.

See the [Envelopes API reference](https://developers.signable.app/openapi/envelopes) for more information.