I have a use case at the moment where a user who is subscribed to an autorenewable subscription can invite a friend and receive a free month. On Google this is pretty straight forward to implement. The problem is on IOS. 

I saw we can use the promotional offers in order to implement this. The problem is that I offer that free plan on the server side and the promotional offers can be purchased only on the mobile app side. Is there any way to purchase a promotional offer on our server side?