e2ee_key_source_unauthorised· reason_code· applies to service_callA backend media SDK supplied an SFrame / frame encryption key from a source other than the Arkret MLS exporter (label `ak.rtc-frame-key/v1`). Clients MUST reject and refuse to publish / subscribe media. Closes the attack where backend cloud key escrow could intercept ostensibly-E2EE media. See zh/crypto-media/media-service-binding.md §8.1.