Hoya platycaulis is very difficult to root, and I lost my first couple specimens from my inability to root it. The secret is to put it into a glass of water for around 3 weeks and when it just starts to form a barely visible root pot it up into whatever media you want to grow it in. If you leave it in the water too long it will not make it.
![](https://i0.wp.com/vermonthoyas.com/vhwp/wp-content/uploads/2019/11/Hoya-platycaulis-113-scaled.jpg?fit=625%2C317&ssl=1)