Q.I purchased a single leaf of Hoya Kerri and it is turning brown
It is a rooted leaf of variegated Hoya Kerri and it started to turn brown on one side but is growing bigger.
Certified GKH Gardening Expert
It is likely that this is a normal process. As the plant replaces its self, that leave will slowly die and drop off. Could you include a photo? This will help me to see what is going on.
I would also make sure to only water when the top of the soil is almost dry. This will ensure that it does not get an infection.
This article will help you to care for these plants: https://www.gardeningknowhow.com/ornamental/vines/hoya-wax-plant/growing-hoya-wax-vines.htm
One possible reason is that your plant is getting too much sunlight.