The phrase "puts a stopper in" implies bringing an end to or halting a particular activity or process. Antonyms for this phrase could include "initiates," "starts," or "enables." These words suggest the opposite action of putting a stopper in something, with a focus on beginning or allowing a process to continue. Other antonyms may include "advances," "facilitates," or "propels," which all imply a movement forward or progress. The choice of antonym depends on the context of the situation and the desired outcome, whether it be progress, stagnation or reversal.