i have face this issue after adding pendingintentflag.immuitable.

I got the same error in my project because of "Starting with Build.VERSION_CODES.S (Android 12), it will be required to explicitly specify the mutability of Pending Intent" and solved with replacing the code by below-

Before code- 

        PendingIntent pendingIntent = PendingIntent.getActivity(this, (int) (Math.random() * 10000), notificationIntent,PendingIntent.FLAG_UPDATE_CURRENT);

Replace code- 

        PendingIntent pendingIntent;
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.S) {
            pendingIntent = PendingIntent.getActivity(this, (int) (Math.random() * 10000), notificationIntent, PendingIntent.FLAG_IMMUTABLE);
        }else{
            pendingIntent = PendingIntent.getActivity(this, (int) (Math.random() * 10000), notificationIntent, PendingIntent.FLAG_UPDATE_CURRENT);
        }

This error message is related to the PendingIntent flags when creating a PendingIntent object. According to the error message, when targeting Android S+ (version 31 and above), you need to specify one of the flags FLAG_IMMUTABLE or FLAG_MUTABLE when creating a PendingIntent object.

FLAG_IMMUTABLE indicates that the PendingIntent should be immutable, and FLAG_MUTABLE indicates that the PendingIntent should be mutable. Mutable PendingIntent objects can be used with inline replies or bubbles.

So, if your app targets Android S+ and you are creating a PendingIntent object, you should use one of these flags when creating the PendingIntent. In your case, you used PendingIntent.FLAG_IMMUTABLE but still received the error. This might be because the PendingIntent is used in a way that requires it to be mutable.

To resolve the issue, you can try using PendingIntent.FLAG_MUTABLE instead of PendingIntent.FLAG_IMMUTABLE. However, if your app does not require the PendingIntent to be mutable, it is better to use PendingIntent.FLAG_IMMUTABLE for better security.