Use URL parameters in Form fields. Dynamic text replacement in form fields.
Disable auto prefill first - "no_prefill": true
<script type="text/javascript">
var tagify = "INSTAPAGE_ALLOW_TAGIFY"
</script>
<script>
ijQuery(document).ready(function($){
if(document.location.search.length) {
ijQuery("input[name='" + base64_encode("Form field name") + "']").attr( 'value','[URLparameter]' );
ijQuery("input[name='" + base64_encode("Form field name") + "']").attr( 'placeholder','[URLparameter]' );
}
});
</script>