A 404 response usually means the PayPal endpoint or route being called does not exist or is incorrect. Double-check the PayPal API URL, verify whether you're using the correct sandbox/live credentials, and ensure the package configuration matches the current PayPal API version. Also review your redirect URL and callback routes, as an invalid endpoint can trigger this error even when the code looks correct. Sharing the exact PayPal package and configuration details would make troubleshooting much easier....