Simple Fix Whatsapp Click to chat (api.whatsapp.com) in Facebook Browser

rename-link.js

<script>
    function isFacebookApp() {
        var ua = navigator.userAgent || navigator.vendor || window.opera;
        return (ua.indexOf("FBAN") > -1) || (ua.indexOf("FBAV") > -1);
    }

    if (isFacebookApp()) {
        var buttons = document.querySelectorAll('a[href*="https://api.whatsapp.com"]');

        [].forEach.call(buttons, function(button) {
          button.href = button.href.replace('https://api.whatsapp.com/', 'whatsapp://')
        });
    }
</script>