A VPN swaps your IP and nothing else. Your canvas hash, WebGL renderer, installed fonts and audio fingerprint stay identical, and that is exactly the bundle Meta hashes into one device ID. An antidetect browser gives every ad account its own isolated browser profile with its own fingerprint and its own proxy, so two accounts never resolve to the same machine. If you buy traffic on more than one account, this is the layer you are missing:
https://rating-antidetect-browser.com