Decryption failed because of a mismatch between the identity keys of the device we received the room key from and the identity keys recorded in the plaintext of the room key to-device message.
The room key is not known
The sender's identity is unverified, but was previously verified.
Other failure.
The room key is known but ratcheted
We weren't able to link the message back to any known device.
The sender device is not cross-signed.
Decryption error codes