disassemble the pump, on the piece that you push down on (idk how else to describe it) there’s an O-ring right at the bottom. frap roast has its own specific o-ring. it’s like an off white, solid piece. other pumps use a clear ring with another blue seal inside. see if you can find the frap roast one and replace it, that solved the problem at my store

It's most definitely caused by the small plastic piece on the bottom of the plunger/piston piece. It is slightly tapered, and the wider part should be facing up, the narrower end should be facing down. If that doesn't solve it, replace that part with a new one. They wear out and need to be replaced occasionally.

Exactly this worked for my store