# outbound_agent_id on PATCH /update-phone-number/{} stops working

Calls to PATCH /update-phone-number/{id}, body parameter outbound_agent_id on Retell AI API stopped working on March 31, 2026.

## What to use instead

Send outbound_agents instead as a list of {agent_id, agent_version, weight} entries whose weights sum to 1. For a single agent, set the weight to 1.

- API: Retell AI API (api.retellai.com)
- Kind: Parameter removal
- Takes effect: March 31, 2026
- Calls after that day: fail
- Calls it hits: `PATCH /update-phone-number/{id}`, `body parameter outbound_agent_id`
- Source: [Announcement](https://docs.retellai.com/deprecation-notice/2026/03-31_phone_number_agent_fields)
- Verified: November 6, 2026, against Retell AI API's own pages
- Page: https://www.okapi.bot/providers/retell-ai-api/breaking-changes/outbound-agent-id-on-patch-update-phone-number-stops-working/

## Retell AI API's words

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

Okapi finds the calls this change hits in your repo and opens the pull request with the fix: https://github.com/apps/okapi-agent