Can I ask user to share his/her email id while doing

We sell magazines through a third party app platform called Pocketmags and our website. The magazines have Print, Digital and Combo options available for purchase. Also, this third party app provides the platform to read the digital version of the magazines.

Once a user buys a subscription on the website, he/she receives the email with the login information on PocketMags, where he registers his login details and can start reading his subscription. With us, the customer shares his billing/shipping address along with their email id while they make payment.

Now we have our own app where through which we want to sell these magazines and have to integrate In-App purchase for selling these digital subscriptions. How do we send the 3rd party subscription access details on email to the user if they do in app purchase?

Can I ask user to share his/her email id while doing
 
 
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