Voice control is not responding
When Siri does not act on a Dimpsy command.
Check the phrasing
Commands resolve against scene names. "Set Dimpsy to campfire" works because Campfire is a scene. "Make it cosy" will not, because nothing is called Cosy.
Check the shortcut was donated
The first time you use a scene in the app, the app offers it to Siri. If you have only ever used the app's own controls, Siri may not know the scene exists yet.
If it still fails
Open Settings, then Siri, then App Intents, and confirm Dimpsy is enabled. Reinstalling the app re-donates every shortcut.