You can use the developer console to send a message to your Octopus device and, for example, change the color of the device's LED:
Navigate to the Things section (left sidebar of the developer console).
Click the row of the thing belonging to your octopus.
Enter the subject setColor defining the meaning of the message. This subject triggers the setting of a specific LED color on an Octopus with version 1.1.0.
Set the message content containing the custom payload in JSON format to define the LED color.
You can vary the numbers for "r" red, "g" green, "b" blue and "w" white between 0 and 255.
Enter the timeout 0 s (= "do not wait for a response").
Open the feature list.
Select the led feature.
Click Send to submit the message.
Your message is sent to the physical device where, where the firmware consumes your entries from step 5 and changes the LED color.
Especially for such scenarios, where you try to remote control an IoT asset, it gets important to get insight if the device is connected and listening at all.