How to Fix Copilot Chat ‘Failed to Send Message’ Error

Official documentation checked October 14, 2026.

When Copilot Chat says “Failed to send message,” preserve the unsent prompt and record the exact error before retrying. The message does not establish whether the request reached the service, which transport failed, or whether an account token expired. Start with a harmless test and the affected client rather than deleting app caches or disabling network protection.

Why Copilot Chat Shows the Failed to Send Message Error

Organizational Copilot Chat has account, subscription, browser, app, and network requirements. The relevant conditions depend on the feature and host. Microsoft’s current requirements describe WSS connectivity for several integrations; they do not map every send-failure message to a single WebSocket handshake or a Microsoft Graph token.

A browser-specific session problem, an interrupted connection, a service incident, or an explicit account or policy failure should be investigated using its actual evidence. If one prompt fails while a simple non-sensitive prompt succeeds, inspect the request, feature, attachments, and any displayed restriction without assuming a universal character or file-size limit.

Steps to Fix the Failed to Send Message Error

1. Preserve and isolate the request

1. Copy unsent text to an approved temporary location if necessary. Check the conversation for an already-submitted prompt or response before repeating the request.
2. Record the time, client, account context, error, and any displayed correlation ID. Do not include authentication tokens or cookie values in support evidence.
3. Try one short, non-sensitive prompt in a new chat using the intended account. Avoid repeated retries of actions that could send messages or change external data.
4. Compare the organization’s approved web entry point and the affected app if both support the feature. The current organizational Copilot app URL is transitioning to copilot.cloud.microsoft; use the official access route rather than assuming every consumer URL is the correct work entry point.

2. Check sign-in and service conditions

Complete any normal sign-in or MFA prompt. For an explicit license-validation error, use Microsoft’s account and browser guidance. Closing browser windows is not a guarantee that all persistent authentication state has been erased.

If multiple users are affected, ask the administrator to check Health > Service health, following the service-health guide. Record an applicable advisory before continuing local resets.

3. Use targeted browser checks

Use a current supported browser. If the issue is confined to one browser session, save unsent work before clearing the affected site’s cookies. Edge’s documented route is Settings > Privacy, search, and services > Cookies > See all cookies and site data: search for the site, expand it, and delete its entry. See Microsoft’s site-specific cookie instructions.

Compare an organization-permitted clean session or profile while retaining the original profile. Private browsing changes cookies and extensions and can also block cookies required for validation; its result does not isolate a single cause. Have IT review managed extension or cookie settings instead of turning off all protections.

4. Investigate network conditions with IT

Microsoft’s requirements call for the current Microsoft 365 and Copilot endpoints and WSS connectivity, including the documented office.com and cloud.microsoft domains. Ask the network team to check the applicable routing, proxy timeouts, and connectivity test results. Do not disconnect a required VPN, turn off the Windows proxy, weaken firewall rules, or create an arbitrary wildcard exception to test the error.

For supported Windows scenarios, Microsoft provides a Copilot connectivity troubleshooter through Get Help. Review its findings and any suggested change with the help desk.

If Copilot Still Shows the Error After the Main Fixes

If only Teams or one desktop app fails, capture that app’s version and compare the supported web feature. Follow a client-specific recovery procedure only when support identifies it. Do not treat the legacy Teams folder or OfficeFileCache as a universal Copilot cache, and do not delete them to repair a generic send error.

Give support the sanitized reproduction, affected users and clients, time, error details, network test results, and whether the simple prompt succeeded. A product support troubleshooter should match the symptom; an Office installation or activation-reset scenario is not automatically relevant.

Copilot Chat Error: Browser Version vs Desktop App Behavior

This article verifies official requirements and safe diagnostic steps. No client, account, network, prompt, or production service was operated on, and the exact generic send-failure phrase has not been reproduced.