Vercel’s response size limit. YouTube streams pieces of video chunks. If a chunk exceeds 50MB (rare for 720p, common for 1080p), the function crashes. Fix: Change YouTube quality settings to 480p or 720p. Alternatively, use the "Corrosion" backend instead of "Bare" for video sites.

Furthermore, hosting a proxy on Vercel that is publicly accessible means you are responsible for the traffic. Users could use your proxy to access illegal content. Always: