Can't say for sure, but you said you've been keeping it on the dry side. At least one source I've read says P. nellii need some water in winter. I know that my own are growing outside now in the soil and got a lot of rain about a month ago. Most of them are doing quite well, flowering frequently and dividing or growing new leaves. Some of them have rotted as well, but I've no idea why. The sick ones are only a few feet or even a few inches away from the healthy.

Pleiospilos' blooms generally only open fully in the afternoon, with some warmth and direct sun. And if the soil is too dry, blooming may also be aborted.

The window of opportunity is only a few days, after that if the conditions have not been met, the flower dries up and you have to wait again until next year. Since you have had it for one month, I can't tell if the bloom was about to open at the time you got it, or if it merely had a flower bud still forming.

Regular watering is also crucial to sustain flower bud development. If watering is inadequate, the plant will use its available resources to stay alive and bypass flowering.

"20 drops of water" is not really the right way to take care of these plants. If you use an appropriate soil mix in a pot, you can drench the soil during active growth and blooming.

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