WhatsApp has started testing "view once" messages on iOS. As the name implies, these will be messages that you send and can only be viewed once by the recipient. After they viewed them once, the messages will disappear.To enable the functionality you will just need to long-tap on the Send button, which will then present you with the option to "Send as view once". Engage that and you're done.WhatsApp initially started testing this feature on Android earlier this month, and now the same is happening on iOS. The view once option is already available for photos, videos, and voice...