Before I load any new resin cartridge into the Form 2 I turn it upside down, remove the orange bite valve cover and push the bite valve with my finger until the slit opens up fully. Some of them you really have to keep pushing with some force before they open at all.
I’d be willing to bet that is your issue… Take the cartridge out (make sure you have closed the top vent) turn it over and check to see if the bite valve is opening fully…push it until it does, reinstall the cartridge and you’ll be good to go…Hopefully !