Considerations for Closing and Reopening Tasks in Salesforce Classic | Salesforce
Suppose that you’ve created a validation rule for closing a task; for example, you require users to enter a comment. Before users can close a task, they must first open the task detail page and edit the task. Likewise, if you’ve set up more than one Open status for tasks, users must edit the task to choose a status when they reopen a task.
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