Android: After creating a new notification, the older one is replaced

You are using a hardcoded id for your notification, of course it will replace the old one. Try using a variable ID instead of a hardcoded 100.

mNotificationManager.notify(100+x, mBuilder.build());

or something of the sort.

Use variable id for notification, I have faced this issue 1 Hour ago And used this technique to overcome this issue.

        val id= Random(System.currentTimeMillis()).nextInt(1000)
        mNotificationManager?.notify(id, mBuilder.build())

for long term solutions, you can use a random method to generate integer variable for you and call that in notify.

mNotificationManager.notify(createRandomCode(7), mBuilder.build());

public int createRandomCode(int codeLength) {
        char[] chars = "1234567890".toCharArray();
        StringBuilder sb = new StringBuilder();
        Random random = new SecureRandom();
        for (int i = 0; i < codeLength; i++) {
            char c = chars[random.nextInt(chars.length)];
            sb.append(c);
        }
        return Integer.parseInt(sb.toString());
    }