Creating the Alert Rule for Purchase order

HI,

I am new to AX 2012 r3, need a help to create the alert rule for Purchase Order, where need an alert for due date of the purchase order before a week.

I tried this by following the below technet link. But I am not getting any alert regarding due dates.

https://technet.microsoft.com/en-us/library/aa497014.aspx

Request your help in resolving the same.

Thanks in advance.

Regards

Kiran