Where the connection failed
Chromium, the browser engine used by Chrome, defines this error as a failure to resolve the proxy server's name or connect a socket to it. The browser needs that connection before it can ask the proxy to fetch a page. A misspelled hostname, an incorrect port or a network that cannot reach the endpoint can therefore leave you at the same error page.
The definition specifically excludes failures during an HTTP proxy's CONNECT request, which is the step used to establish a tunnel for an HTTPS website. Read the exact error before changing settings: a connection failure, a tunnel failure and an authentication response send you to different checks.
| What you see | What it tells you | Check next |
|---|---|---|
| ERR_PROXY_CONNECTION_FAILED | The proxy address could not be resolved or connected to | Host, port, active configuration and network path |
| HTTP 407 | An HTTP proxy requested authentication | Whether the client supplied valid proxy credentials |
| ERR_TUNNEL_CONNECTION_FAILED | A tunnel through the proxy could not be established | The proxy's response to the tunnel request |
| A website returns an HTTP error | You have a response to inspect; the sender still matters | Response details before assuming a local connection failure |
1. Copy the host and port from the right resource
Open the connection details for the proxy you intend to use. Compare the host and port with the saved browser profile. Remove spaces, check every digit of the port, and make sure the host field contains only the host when the app provides separate fields. A full connection line pasted into a host-only box is a different input.
For IPMusk Rotating Residential, the gateway is gate.ipmusk.com and the port is 31212. Static ISP and Datacenter resources use their own assigned host and port. Do not substitute the Residential gateway for a static address. ipinfo.io is a destination used to check an exit IP, not the proxy gateway.
An address such as 127.0.0.1 points back to your own computer. If your settings name it, you are connecting to a local proxy application first. Confirm that application is running and listening on the port in the browser settings. A remote provider cannot repair a stopped listener on your computer.
2. Find the settings the browser is using
Write down the existing configuration before editing it. Then check the browser profile, any proxy extension and the operating system's proxy settings. A change in one place is not proof that the profile you launched uses it. Inspect the profile that actually shows the error, especially if you keep several profiles with similar names.
On Windows, open Settings, then Network & internet, then Proxy. Look at the manual server, setup-script address and automatic configuration options. Microsoft also documents separate proxy settings for VPN connections, so inspect those if that is the connection you are using.
On a Mac, open System Settings and Network, select the active network service, then Details and Proxies. Review the enabled proxy types and any automatic configuration URL. Wi-Fi and another network service may have different settings; edit the service carrying the affected connection.
For an extension or a dedicated browser profile, compare its enabled configuration with the one you intended to test. Reopen the affected profile after saving. If an organization manages the settings, ask its administrator to check them rather than trying to override the policy.
3. Match the protocol and authentication method
Once the endpoint is correct, verify whether the client is meant to speak HTTP or SOCKS5 to it. An HTTPS destination does not by itself mean you should choose an HTTPS proxy. An HTTP proxy can carry HTTPS website traffic through a CONNECT tunnel; the proxy protocol describes the connection to the proxy server.
Authentication support also depends on the client. Chromium's documentation says native Chrome SOCKS5 proxying does not support SOCKS5 authentication. If your service requires a username and password, a bare Chrome SOCKS5 setting is not sufficient. Use a client that explicitly supports the required authenticated protocol, or the service's HTTP option where supported.
Chrome also ignores credentials embedded in its manual proxy-server settings. Pasting a username and password into that server address is not a reliable way to configure authentication. Use your client's documented authentication fields or supported login flow. If the error becomes 407, follow the separate authentication guide instead of continuing to treat it as an unreachable port.
4. Compare one endpoint from two places
Use one proxy endpoint and a simple public page while diagnosing. Avoid signed-in services during connection checks, and change one setting at a time so the result remains useful. A direct browsing test, if permitted on your network, can establish whether ordinary internet access works. It does not prove the proxy works, and it sends that request without the proxy.
The IPMusk port checker attempts a TCP connection from a Cloudflare server. An open result means that server reached the port. It does not check your password, complete a proxy request or prove that your own network can reach it. The tool cannot test a listener on 127.0.0.1 or another private address.
If the remote check reaches the port while your browser cannot, inspect local DNS, the effective settings and your network's outbound rules. A firewall may allow normal website traffic but restrict the proxy's port. Ask the network administrator about the specific endpoint; turning off security software is not a useful diagnosis.
The proxy checker goes further by attempting a proxy connection with the selected protocol and supplied credentials. Its result still describes a test from the service's network, not your computer. A failure from both places is evidence to investigate the endpoint, not enough to name a provider outage. If appropriate, compare the same configuration on another network you are allowed to use.
Verify the repair and send useful evidence
After the page loads, check the visible exit IP from inside the affected browser profile. A page can load through a direct connection or a bypass rule, so loading alone does not confirm that the intended proxy carried the request. Compare the exit with the configuration you selected before returning to your normal work.
If it still fails, send support the time and time zone, browser version, operating system, product or resource ID, and exact error text. Include whether the port checker and proxy checker ran, where they ran from, and their results. Redact passwords and full connection URLs from every screenshot or attachment. Keep the current settings recorded so support can compare the failing configuration with any later change.