dude throw this device away they dont do anything except potentially hurt you. i tried it a few times my dick is still 6.3 inches nomatter what i did. your dick is what it is and thats all itll ever be so OWN IT!
Spread some lube around the rubber seal and press down pretty hard when you start pumping. Also, if you are using a cock ring it can ONLY be around your cock shaft. You can't have it pass under your balls or you won't get a seal. You have to be reasonably hair free as well. Otherwise, it may just be your pump has a leak in it.