How can I troubleshoot a 403 Access Denied error with a proxy?

First, verify the proxy server is working correctly. Try accessing a different website through the same proxy. If that works, the issue is likely with the target website. Check the proxy's configuration, ensuring it's allowed to access the website. Also, try a different proxy server – some proxies are more reliable or less likely to be blocked. Review the website's terms of service regarding proxy usage.