Use URL parameters in Form fields. Dynamic text replacement in form fields. !Disable auto prefill first - "no_prefill": true
Example: http://dtrinfields.pagedemo.co/
<!-- START code for DTR in form fields -->
<script type="text/javascript">
var tagify = "INSTAPAGE_ALLOW_TAGIFY"
</script>
<script>
document.addEventListener("DOMContentLoaded", function() {
function pageGenerator(fieldName){
return window.__page_generator ? fieldName : base64_encode(fieldName);
}
if(document.location.search.length) {
document.querySelector("input[name='" + pageGenerator("First name") + "']").value = '[fname]';
document.querySelector("input[name='" + pageGenerator("Last name") + "']").value = '[lname]';
}
});
</script>
<!-- END code for DTR in form fields -->
<!-- START code for DTR in form fields -->
<script type="text/javascript">
var tagify = "INSTAPAGE_ALLOW_TAGIFY"
</script>
<script>
document.addEventListener("DOMContentLoaded", function() {
if(document.location.search.length) {
document.querySelector('input[name="First name"]').value = '[fname]';
document.querySelector('input[name="Last name"]').value = '[lname]';
}
});
</script>
<!-- END code for DTR in form fields -->