Copilot Chat (Microsoft 365 business) New Agent Error 400

Jenish Pokhrel A 400 (Bad Request) error when creating a new agent in Microsoft 365 Copilot Chat is usually caused by one of the following:

1. Licensing issue (most common) Agent Builder in Microsoft 365 Copilot requires a Microsoft 365 Copilot license assigned to your account. Verify your license in the Microsoft 365 Admin Center under Users → Active users → your account → Licenses.

2. Agent creation disabled by admin policy An admin may have restricted who can create agents. Ask your Microsoft 365 admin to check:

• Microsoft 365 Admin Center → Copilot → Settings — ensure agent creation is enabled for your user or group.

3. Tenant not yet provisioned If the Copilot license was recently assigned, it can take up to 24 hours for the service to fully provision. Try again after waiting.

4. Browser/cache issue Try:

• Hard refresh (Ctrl + Shift + R)
• Clear browser cache and cookies
• Try a different browser or InPrivate/Incognito window

Agent Builder in Microsoft 365 Copilot Chat is a built-in feature that lets users create agents directly from the Copilot Chat experience. The error shown (HTTP 400) occurs while trying to open the New agent experience, which relies on this embedded agent builder.

To create agents successfully in Microsoft 365 business environments, ensure the following conditions are met:

1. Use supported entry points
   • Open Copilot Chat from one of the supported surfaces:
     • microsoft365.com/chat or office.com/chat (Microsoft 365 Copilot Chat)
     • Microsoft Teams desktop or web client.
   • In these surfaces, use the Create an agent / New agent option in the Copilot Chat right rail or the Agents section.
2. Confirm feature availability and licensing
   • Agent Builder in Copilot Chat is available for Microsoft 365 commercial customers as part of the Copilot Chat experience and adds pay-as-you-go agents on top of the free chat.
   • For full Microsoft 365 Copilot capabilities (including embedded Copilot features in Word, Excel, Outlook, and Teams, plus custom agents), the organization must have a Microsoft 365 Business or Enterprise plan with Microsoft 365 Copilot.
   • If the tenant only has Microsoft 365 Copilot Chat (no Microsoft 365 Copilot), only the capabilities listed for that option are available. Admins must enable and govern agents accordingly.
3. Work with the admin if issues persist
   • Because agent creation and usage are governed by Microsoft 365 and Copilot Studio admin controls, a 400 error when opening New agent can indicate a tenant-level configuration or governance issue rather than a client/browser problem.
   • Provide the admin with the Session ID shown on the error screen so they can:
     • Verify that Microsoft 365 Copilot Chat and agent capabilities are enabled for the user.
     • Check Copilot-related governance and security settings in Microsoft 365 and Copilot Studio.
     • Escalate to Microsoft Support if necessary, using the Session ID and time of failure.

Once the admin confirms that Copilot Chat agents are enabled and the tenant meets the minimum requirements, the New agent flow in Copilot Chat should open without the 400 error, allowing creation, configuration, testing, and sharing of agents.

References:

• Agent Builder in Microsoft 365 Copilot
• Use Agent Builder in Copilot Chat
• Create Copilot agents in Microsoft 365 Business Chat and Teams
• Agents admin guide for Microsoft 365
• Latest updates in Copilot Chat