workflowId: null to remove the IVR assignment. Assigning a different active IVR replaces the previous IVR for that number. Changes apply to new calls.
Requires both phone:write and workflows:write scopes. Telephony and Classical IVR must be enabled. The workflow must be active, use the ivr-incoming-call trigger and belong to the same organization as the number.
See Classical IVR setup for activation and real-call testing.