My mistake, you can’t do render field based on the field key. You can only do it generically for every field or for a specific field type. You need to check for the field you want to add the html to in the function.
add_action('acf/render_field', 'add_address_heading', 1, 1);
function add_address_heading($field) {
if (is_admin()) {
// only on the front end
return;
}
if ($field['key'] == 'field_573d84b07da66') {
?><h2>Address</h2><?php
}
}
