Client.subscribe callbacks. First argument will be an error if an error occurred (such as a timeout) or null. Message argument is the received message (which should be treated as debug information when an error is provided).
Client.subscribe callbacks. First argument will be an error if an error occurred (such as a timeout) or null. Message argument is the received message (which should be treated as debug information when an error is provided).
Client.subscribe callbacks. First argument will be an error if an error occurred (such as a timeout) or null. Message argument is the received message (which should be treated as debug information when an error is provided).