You are trying to send these media files from your App <AppName> which is not LIVE yet using our Sandbox. Sandbox API is limited and only supports sending text message and media message given below:
2. https://www.buildquickbots.com/whatsapp/media/sample/png/sample02.png File:
This restriction is kept for media messages due to security reasons. You will be able to send all supported media messages when your app will be Live with your business phone number. Hence, using any other URL in Sandbox mode for sending media will give you an error message that Media Url Not WhiteListed.