Validate allows you to check work submitted by a partner before the work is marked as complete. Validation is always enabled for the Collaboration - simple task type, and is optional for the Collaboration - full task type.
If validation is active, the task status will be set to Submitted when the partner submits their work. If validation is not active, the task status will be set to Complete.
Look in the Run section of Task details to view the response. If required, use Chat to clarify what they have sent you.
Then use the Validate section of Task details to indicate whether you accept the task, or whether you require rework.
The message is optional if you accept the task, and mandatory if you ask for rework. Submit the validation.
If you accept the task, the task status will be set to Complete. If you ask for rework, the task status will be set to Redo. The partner will be sent a notification, and if rework has been requested they will be able to continue with the work and resubmit it.