Zoom Phone showing Error Code 408 usually means the call setup did not get a response in time, so the app reports a request time out and asks you to check the network and try again.[✅Source-1]
How This Page Helps You Fix Error 408
This guide focuses on practical fixes that work in real networks: Wi-Fi, ethernet, mobile hotspots, office firewalls, and desk phones. Each step is written for a person who needs stable calling, not for a lab environment.
Good to know: some call failure popups show a longer number (example: 2202408). The last 3 digits are the error code you troubleshoot.
If the issue happens only on one network (office Wi-Fi but not mobile hotspot), the fastest path is to check network filtering, proxy behavior, and real-time traffic handling.
Table of Contents
Understanding Error Code 408 in Zoom Phone
408 is a standard SIP response meaning Request Timeout: a request was sent, but a timely response did not arrive, so the transaction ends as a timeout.[✅Source-2]
In everyday terms, your device tried to set up a call, but something in the path (Wi-Fi, router, VPN, proxy, firewall, DNS, or upstream network) delayed or blocked the signaling long enough that Zoom Phone stopped waiting.
What You Usually Notice
- The call fails before ringing, and you see 408 or a message that mentions timed out.
- It works on a different network (mobile hotspot) but fails on the current one, which points to a network path issue.
- Desk phones may show slow registration or intermittent calling when real-time traffic is delayed.
Common Triggers That Lead to 408
A timeout is not one single problem. It is the final symptom after a request gets stuck. These are the most frequent reasons in a Zoom Phone environment.
Network Path Issues
- Unstable Wi-Fi (high jitter, brief drops) causing signaling delays and retries.
- Router features that interfere with VoIP traffic (often called SIP ALG on consumer gear).
- Captive portals and content filters that allow web browsing but delay real-time sessions.
Security And Inspection Issues
- Corporate web proxies inspecting or buffering traffic that should flow directly in real time.
- Firewall rules that allow general internet but restrict UDP behavior needed for voice media.
- VPN routes that increase latency or break return traffic consistency.
Cause And Check Map
| Trigger | Why It Can Produce 408 | What To Check First |
|---|---|---|
| Proxy Inspection | Inspection can add delay, reorder packets, or block direct paths that SIP and voice flows expect. | Try bypassing the proxy for Zoom Phone traffic or test from an unproxied network. |
| VPN Routing | Extra hops and split tunneling can cause slow signaling or inconsistent return traffic. | Temporarily disconnect VPN and retry the call with the same number. |
| Wi-Fi Instability | Short drops look like silence to the app, so it waits, retries, then times out. | Switch to ethernet or a different Wi-Fi access point; retest. |
| Firewall Filtering | Outbound traffic may leave, but replies or UDP behavior may be restricted, delaying setup. | Compare behavior across networks; review allowlists for required destinations. |
| Device Compatibility | Older firmware or missing security capabilities can disrupt registration and call setup. | Update firmware and confirm TLS 1.2 support on desk phones. |
Fast User Fixes for Zoom Phone 408
Start with steps that change one variable at a time. That makes the root cause obvious instead of hidden behind multiple changes. Keep notes on what you tried and what changed in the call result.
- Switch Networks Once
Use a mobile hotspot (or a different Wi-Fi) and try the same call again. If it works, your original network is the likely cause, not the account or number. This is the quickest isolation test. - Restart the App and the Network Edge
Close the Zoom app fully, reopen it, and retry. If you are on a home router, reboot the router as well. A clean reconnect can remove stale sessions and temporary routing issues. - Disable VPN and “Smart” Network Tools Temporarily
Turn off VPN, “secure web” tools, or traffic accelerators, then test again. These tools can be helpful for browsing, but voice setup needs predictable network timing. - Try Ethernet If Possible
A quick wired test removes Wi-Fi interference from the equation. If ethernet fixes it, focus on Wi-Fi signal, access point load, and roaming behavior. - Sign Out and Sign In
Signing out refreshes tokens and service connections. It is a simple reset that can clear a stuck client state without changing any settings.
If Calls Fail Only on Office Networks
When the same device works on a hotspot but fails at work, the next focus is inspection and filtering. Zoom notes that web proxies can introduce latency, jitter, and packet loss for real-time applications, and recommends bypassing web proxies for Zoom Phone traffic so it routes directly to Zoom data centers.[✅Source-3]
Network And Admin Checks That Fix 408
These items are for IT or anyone who can adjust network settings. The goal is to ensure timely signaling and consistent voice media routing, especially when firewalls, proxies, or segmentation are present.
Check Proxy Behavior for Real-Time Traffic
- Confirm whether Zoom Phone signaling or voice is being forced through a web proxy or SSL inspection layer; if yes, test a bypass for real-time traffic.
- If bypass is not possible, test allowing UDP routing behavior as recommended by your network policy, then compare call setup success and delay.
- Verify that the client can maintain stable connectivity without frequent reconnects; repeated reconnects can raise the likelihood of timeouts.
Confirm Source Port Ranges When Port-Based Policies Exist
If your network classifies traffic by source ports, Zoom provides an admin setting to choose the media source port range for Zoom Phone calls on desktop and mobile apps. The range must be between 9000 and 9999, and at least 50 ports should be configured to avoid impacting functionality.[✅Source-4]
Port-based rules that are too narrow can create a partial allowance: some calls start, some fail, and many fail as 408 because the return path is inconsistent.
Review Segmentation and Filtering on Every Hop
- Check VLAN rules, inter-VLAN ACLs, and Wi-Fi guest isolation. A call may fail if the client can reach the internet but cannot maintain the same quality across all segments.
- Confirm that DNS resolution is fast and consistent. Slow DNS can delay initial connections, which can show up as a timeout in the app.
- Look for security tools that “hold” unknown UDP flows. Even brief holding can trigger a 408 during call setup.
Keep the Goal Simple: Stable Connection and Open Required Paths
Zoom’s network guidance for Zoom Phone emphasizes that users need a working internet connection and that the necessary network ports must not be blocked so the client can maintain an active connection to Zoom Phone data centers.[✅Source-5]
Desk Phone Checks for Zoom Phone 408
Desk phones add a few extra variables: provisioning, firmware, and security support. If desk phones are involved, check these before deep network changes.
- Confirm Firmware Is Current
Older firmware can behave unpredictably under modern network security. A small update can restore reliable registration and call setup. - Verify TLS Support
Zoom notes that desk phones must support TLSv1.2 to work with Zoom Phone, and using the latest firmware is part of proper operation.[✅Source-6] - Retest from a Clean Network Segment
Place one desk phone on a known-good segment (or temporary allowlist policy) and test. If the call succeeds, you have a strong sign the original segment needs policy adjustments.
Optional: If You Use Zoom Phone Local Survivability
Organizations using the Local Survivability module should also confirm the module-specific firewall rules are present, including required TCP and UDP ranges shown in Zoom’s survivability firewall documentation.[✅Source-7]
This matters because a survivability design adds more network hops and policy points. A missed rule can look like a timeout even when general internet access is fine.
What To Share With Your Zoom Phone Admin or IT Team
When Error 408 persists after basic tests, the fastest resolution often comes from sharing clean, specific details. These items reduce back-and-forth and point directly to the failing layer.
- The exact message and the last 3 digits of any longer call failure code (example: …408).
- Where it fails: office Wi-Fi, home Wi-Fi, ethernet, mobile hotspot (include which one works as the control test).
- Client type and version: desktop app, mobile app, or desk phone model + firmware.
- Whether VPN, web proxy, SSL inspection, or secure web gateways are enabled on the failing network.
- Time window and frequency: “every call” vs “intermittent,” plus any pattern (first call fails, second succeeds, etc.).
FAQ
Does Error Code 408 mean my number is blocked?
Usually no. 408 points to a timeout during call setup. If the call works on another network with the same account and number, it strongly suggests a network path issue rather than a number-level restriction.
Why does it work on a hotspot but not on office Wi-Fi?
A hotspot test removes your office firewall, proxy, and Wi-Fi policies. When that test succeeds, the most likely causes are filtering, inspection, or Wi-Fi instability on the office side.
Should I keep using a VPN if I see 408?
If a VPN is optional, a good test is to disconnect it briefly and retry. A VPN can change routing and timing, which may increase the chance of timeouts during call setup.
What is the simplest admin-side change that often resolves 408?
Start by verifying that real-time Zoom Phone traffic is not forced through a web proxy or heavy inspection, and that required paths are allowed consistently across all network segments. Small changes here often have a large impact on call setup reliability.
Can desk phones cause 408 even if the network is fine?
Yes, if the device is outdated or lacks required security support. Confirm current firmware and that the phone supports TLS 1.2, then retest on a known-good segment to separate device variables from network variables.