"Pay the piper" is an idiom that refers to the consequence of not fulfilling one's duties or obligations. There are various synonyms that can be used in place of this colloquial phrase. For instance, "face the music" refers to accepting the negative consequences of one's actions. "Reap what you sow" implies that one will experience the consequences of their actions eventually. "Comeuppance" refers to getting what is deserved typically because of misdeeds. "Take the fall" is another term used when someone takes the blame for something that they did not do or shoulder the responsibility for something that they did. These phrases can effectively convey the same message as "pay the piper" in different contexts.