After updating:

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.btcontract.walletfiat/com.btcontract.walletfiat.MainActivity}: java.lang.IllegalArgumentException: com.btcontract.walletfiat: Targeting S+ (version 31 and above) requires that one of FLAG_IMMUTABLE or FLAG_MUTABLE be specified when creating a PendingIntent. Strongly consider using FLAG_IMMUTABLE, only use FLAG_MUTABLE if some functionality depends on the PendingIntent being mutable, e.g. if it needs to be used with inline replies or bubbles. at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3645) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3782) at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:101) at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)