International pay per use activation

I assume that this person is on a postpaid plan. Prepaid does not roam in India at all.

     Since you are indicating this person has no service at all I am wondering if they have an incompatible phone, or incompatible service.

   If you log into your account, select the users line, select features add ons.  $0 travel pay-per use should be listed as one of the features. Checking the box next to that feature should permit it on the line.

I strongly advise adding international day pass. This will of course override pay per use and charge a $10 per day charge for even minimal usage. The cost for international data is $2.05 per megabyte. Calls can be $3 a minute or more text messages sent are 50 cents multimedia messages sent or $1.30. But it's the day that it gets you $2 and $0.05 per megabyte can add up very quickly to hundreds or thousands of dollars

And that the user has a phone that is compatible with global service. For example most flagship phones, iPhones, have connectivity bands that will work anywhere. Bargain Androids sold for AT&T prepaid are meant to work in North America and will likely not work outside of North America.