Can someone provide some documentation or tutorial on how to do this? I already know to use UIActivityViewController to compose a text message but I can't seem to find how to compose a link on the message that opens my app and sends data when it's clicked.
You have to implement deeplinking in your application and send the desired data in the text message. when user click on that link, your application open and you have to handle the data from the URL.
find the desent article below about deeplinking and universal link.
https://medium.com/@stasost/ios-how-to-open-deep-links-notifications-and-shortcuts-253fb38e1696