the.com/rain check

means A promise to accept an offer or invitation later instead of now, used literally for rescheduled events or loosely as a polite 'maybe next time.'

from Comes straight from American baseball: in the 1880s, ballparks began issuing fans a literal 'rain check' ticket stub if a game was called off due to rain, letting them attend a future game for free. The term jumped from stadiums to stores in the early 1900s, when shops offered 'rain checks' letting customers buy a sold-out sale item later at the same price. From there it soaked into everyday speech as a courteous way to defer any invitation.