Have you read the page in the docs about working with messages? That will show you how to use the debug node and debug panel to understand the whole message.
Take a look at the topic in that message you posted here, and the topics described in the Shelly API documentation. Are you subscribing to the correct topics? The message you posted here isn't a status message, so it won't have that information you're looking for.
I just found the solution... I thought I could edit the "Will topic". With "shellies/shelly1-
689B68/relay/0" it works just fine, giving me "on" or "off" via payload