Hi there. I am currently building an IOS 12 app and I wanted to know how to program an expiration date into it. The app will function as a digital membership card. After a person downloads it, I would like it to stop working after period of time, say 6 months after its downloaded. So for example someone downloads it on January 1st it will expire on June 1st, and if another person downloads it on march 1st it would expire on September 1st. How would I go about doing this? Relatively new to this. Thank you in advance.