Update payjoin.swift

ios/app/payjoin.swift

@@ -0,0 +1,23 @@
+import UIKit
+import PayJoin
+
+class ViewController: UIViewController {
+    let payJoinService = PayJoinService()
+
+    override func viewDidLoad() {
+        super.viewDidLoad()
+
+        let payJoinButton = UIButton(type: .system)
+        payJoinButton.setTitle("Initiate PayJoin", for: .normal)
+        payJoinButton.addTarget(self, action: #selector(initiatePayJoin), for: .touchUpInside)
+        view.addSubview(payJoinButton)
+    }
+
+    @objc func initiatePayJoin() {
+        DispatchQueue.global().async {
+            let transactionData = Any() // Prepare transaction data
+            let response = self.payJoinService.initiatePayJoinTransaction(transactionData: transactionData)
+            // Handle response
+        }
+    }
+}