The CA certificate and server certificate for the broker running at [test.mosquitto.org] has been updated to use a stronger key. This means that if you have downloaded the CA certificate, you will need to do so again. Likewise, if you have used the [client certificate generator] then your certificate will no longer be accepted and you must generate a new one. [test.mosquitto.org]: https://test.mosquitto.org [client certificate generator]: https://test.mosquitto.org/ssl/