WithHeldCode

the user/device was blacklisted.

the user/devices is unverified.

the user/device is not allowed have the key. For example, this would usually be sent in response to a key request if the user was not in the room when the message was sent.

Sent in reply to a key request if the device that the key is requested from does not have the requested key.

An olm session could not be established. This may happen, for example, if the sender was unable to obtain a one-time key from the recipient.