# inbound_sms_agent_id on POST /create-phone-number stops working

Calls to POST /create-phone-number, body parameter inbound_sms_agent_id on Retell AI API stopped working on March 31, 2026.

- API: Retell AI API (api.retellai.com)
- Kind: Endpoint removal
- Takes effect: March 31, 2026
- Calls after that day: fail
- Calls it hits: `POST /create-phone-number`, `body parameter inbound_sms_agent_id`
- Source: [Announcement](https://docs.retellai.com/deprecation-notice/2026/03-31_phone_number_agent_fields)
- Page: https://www.okapi.bot/providers/retell-ai-api/breaking-changes/inbound-sms-agent-id-on-post-create-phone-number-stops-working/

## What to use instead

Send inbound_sms_agents instead: a list of {agent_id, agent_version, weight} entries whose weights sum to 1 (one agent: weight 1).

## Retell AI API's words

> After 03/31/2026, the deprecated single-agent fields will no longer be supported.