Grid view order button calls server side first and client after server side code

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ASP.NET

In a grid view I have an order button(Link Button). Here when the user clicks on the order button, It has to send one random number to the user mobile and popup a confirmation window(In confirmation window user is going to enter the random number and clicks on ok). Then only the order has to confirm.

But in above scenario, I am not able to send the random number to the user when he clicks on the order button (Problem : here the random number is sending to the user once he clicks on the confirmation window (Popup) "ok" button.)