Lightning Sync で Microsoft Exchange の Oauth 2.0 認証を設定する際、既存の Cookie による問題でエラーが発生することがあります。
Office 365 にログイン後、400 エラーが表示される場合、ブラウザの Cookie を削除するか、プライベートブラウジングを使用して再度認証を試みてください。
また、ブラウザの信頼済みサイトに login.salesforce.com を追加することも有効です。これでも解決しない場合は、一時的にブラウザのセキュリティ設定を低くして認証を完了させてください。
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