Struggling to add custom graph to my plugin

Yup, that’s what I’ve done - the code is here : falken/checkmk-hp-officejet - Codeberg.org

“Services of host” lists

OK	HP Officejet Black	[Open the action menu]
	Black 50% remaining	22 h	12.1 s	
OK	HP Officejet Cyan	[Open the action menu]
	Cyan 60% remaining	22 h	12.1 s	
OK	HP Officejet Magenta	[Open the action menu]
	Magenta 40% remaining	22 h	12.1 s	
OK	HP Officejet Yellow	[Open the action menu]
	Yellow 30% remaining	22 h	12.1 s

But I can’t find my graph anywhere, or even a message saying it’s not drawn for some reason.

Is there a way to debug this? Or have a made a stupid typo somewhere ?!?