My queen of the night began to flower few years ago, then it stopped and began to flower(2) last year. This year it started up good with 3 buds but they all turned brown.
It could be that they lack fertilization. This can happen if it is not maintained yearly. This article will help with the care of these: https://www.gardeningknowhow.com/ornamental/cacti-succulents/night-blooming-cereus/night-blooming-cereus.htm