Scribbled Invoice is a Note in Deathloop .
Location
Found on a desk next to the door in the auto-asphyxiation room in Cass's Apartment in Updaam during the Morning.
Transcript
Cass,
It's set up like you asked, ready to ruin Vanya and Anatoly's First Day.
Which is kind of a dick move, you know? I mean, only reason I agreed to this is the Loop. I'm no murderer.
Anyway, you know what you owe me. I expect it tomorrow. Next loop, I mean. Whatever.
Remember - yellow pipe is the safe pipe. And leave the button alone, or you're like as not to smoke yourself dead instead.
— Brotsky
Colt Note
Two of three hoses on the smoking device will kill the user, but which pipe is safe can be changed.