To watch it on just another muse, you'd have to make a donation (I do not think the amount matters) to become a member. I did it like a year ago, so I am a member now. They have their reasons, which I view as legitimate, for making their site private.
Muse has subbed this. I think you have to be a member though to view it. I don't know how it works now with the whole virus happening. Becoming a member that is.
https://asianvote.net/drama/khun-phaen-begins
https://justanothermuse.com/khun-phaen-begins/