The entrance fee for Sticky Waterfall (Bua Thong Waterfall) near Chiang Mai is free for all visitors, both Thai and foreign[1].
There is a checkpoint before the entrance where staff may ask about the number of people and your country of origin, but this is only for research purposes; no payment is required[1].
You will find ample parking at the site, and from the parking area, it is a short walk to the viewpoint and the top of the waterfall[1].