To apply leave request , when you enter application ,you have to go into Leave ,first.
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As the second step, click the Request Leave.
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After entering this step, you have to choose what kind of leave type you want to request and the date when you want to take leave.
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When you finish all these steps, the last thing you have to do is  adding the reason at the Add Message box as shown in picture and just click the Send Request Button.