---
agentTools:
  projectIndex: https://developer.bill.com/llms.txt
---

# MFA API changes

BILL has removed the ability to add or use a secondary phone number for the BILL v3 API MFA operations.

## Add phone for MFA setup

In the `POST /v3/mfa/setup` API endpoint, BILL has removed the ability to add a secondary phone number for MFA operations. In the API request, `primary` can be set only as `true`. In addition, this field is no longer required in the API request.

When you set `primary` as `false` in your API request, you will get an HTTP 400 response and an error message.

## Generate MFA challenge

In the `POST /v3/mfa/challenge` API endpoint, BILL has removed the ability to use a secondary phone number for generating an MFA challenge. In the API request, `useBackup` can be set only as `false`. In addition, this field is no longer required in the API request.

When you set `useBackup` as `true` in your API request, you will get an HTTP 400 response and an error message.