You are preparing your client for a migration of two workspaces into a grid.

The correct answer is C. The pre-migration report specifically flags the issue under Duplicated and Illegal Usernames, so the immediate defect to resolve is the duplicated username. Because the same username exists in both migrating workspaces but the email addresses are different, Slack cannot treat the records as the same clean identity without addressing the username conflict. Changing one of the usernames removes the duplicate username condition before the migration proceeds. Option A is too destructive and could remove a legitimate user account. Option B is irrelevant because converting the user to a multi-channel guest does not resolve duplicate or illegal username status. Option D may be relevant to identity hygiene in other migration scenarios, especially when preventing duplicate users through SSO alignment, but the question’s report category is specifically username duplication. The consultant should distinguish between user identity matching and username validity. Here, the recommended remediation is to make the usernames unique so the migration report no longer flags the user under duplicated or illegal usernames.