The reference document says the units should be stipulated as KILOPASCALS to read the pressure in kilopascals. That didn't work for me. I tried 'KILOPASCAL' instead, and that worked!
It appears there is an error in the documentation. ?
Thanks for bringing this to our attention @palooster! I have submitted a correction:
The library reference content on the arduino.cc website is updated periodically by an automated system, so the error won't be corrected there immediately, but the correction is under way now and others should not encounter the same confusion as you did in the future.