Almost every listing for PSL-Display fonts across font databases and download sites includes a clear and consistent licensing restriction: or "授权方式：商用须授权 (Commercial use requires authorization)" . This is not an open-source font nor is it free for commercial use.
For alternative modern Thai fonts often used in design, you might also look at (the official Thai government font) or Sukhumvit (used by Apple). psl-display font thai