First, check the o-ring. If there is any flattening, replace it. Rub it with a damp finger, if you get anything coming off, replace it. If you have to keep pressure on the lid to prevent leaks, the ring is probably old & too hard.
Frequently you can run the pressure up to seal the O-ring, then serve at a lower pressure. If you force carbonate at 30 psi, that should set the ring.
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
"I would like to die on Mars, just not on impact." Elon Musk