The absurdity of being asked to feel passionate about invoice processing is almost comedic - it's like being told to fall in love with a spreadsheet. Your manager probably doesn't realize they're essentially asking you to perform enthusiasm for something that's inherently mundane, which says more about corporate culture's disconnect from reality than your work ethic. Maybe you can channel your passion into doing the work well rather than pretending to love accounts receivable - competence often speaks louder than forced enthusiasm anyway.