1038: Part not sendable.

HTTP status: 422. May also be reported as a field-level finding in error.details[].

The part at param is a real type (for example interactive_reply, order, referral, system, unsupported) that only arrives from customers and cannot be sent.

• Use a sendable part type; GET /v1/openapi.yaml marks which are outbound.

• Part schemas
• Sending messages guide