Microsoft 365 Copilot operates within the security, compliance, and identity boundaries of a Microsoft 365 tenant. Shared prompts, prompt links, and Copilot artifacts are governed by organizational access controls and tenant isolation. If a prompt is created and shared from outside your organization, cross-tenant access may not be supported depending on the sharing configuration and administrative policies.

When a user attempts to open a prompt that resides in another organization's tenant without proper cross-tenant sharing permissions, Copilot cannot locate or validate the resource within the user's own environment. As a result, the system displays a ''Prompt not found'' message.

Option B would typically result in an access or permissions error rather than the prompt being unavailable entirely. Sensitivity labels and scheduled prompts do not inherently cause a ''not found'' error. Therefore, the most likely cause is that the prompt exists outside your organization's tenant boundary and is not accessible to you.

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