Pork belly Skin Not Crisping Up

Followed this recipe to a tee, https://www.madewithlau.com/recipes/siu-yuk-crispy-pork-belly, not sure where I went wrong. Pork belly skin is charring in the oven, skin is already black on the edges, and moving to the center. Started it at 350 F, then switched to 400 F, and then 425 F, only a few bubbles have formed. I actually let the pork belly cook about 15 min longer additionally at high heat, but the bubbles did not want to form, and it continued to burn. Any suggestions on where it could have gone wrong? submitted by /u/Nice_Average8846