Notification action icon was not showing

I am trying to show a notification on Android and use the code from this link . In some sources, people said that the icon should be completely white, and some source said that I should use .png instead of vector.

I try all of this, but nobody helped me.

I am trying this code:

Notification newMessageNotification =
    new Notification.Builder(mContext)
            .setSmallIcon(R.drawable.ic_message)
            .setContentTitle(getString(R.string.title))
            .setContentText(getString(R.string.content))
            .addAction(action))
            .build();