X API v2 splits authentication into Bearer tokens (app-only, works for some read endpoints) and OAuth 1.0a/2.0 user context (required for account-scoped data). Your Bearer token can authenticate successfully and still 403 on /2/users/me because that endpoint forbids app-only auth — the 403 isn't a credential failure, it's a context mismatch. Diagnose by checking which auth mode the specific endpoint requires, not whether the token is valid.
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