How to add the contact form to a template manually rather than use shortcode in a page and add a hidden field.
This will be a field in the email, not in the subject
Use this code:
<?php
$property_ref_num = get_post_meta($post->ID,'mls_no',true);
if ( isset($si_contact_form) ) {
echo $si_contact_form->si_contact_form_short_code( array( 'form' => '1','hidden' => "Property=$property_ref_num" ) );
}
?>
Be sure to set the correct form number for example, for form 2 you have to set: ‘form’ =>’2′
Note: with the plugin versions 4.x and higher, you have to enable the setting “Enable PHP sessions” on the form edit “Advanced” tab or this feature is ignored. If you enable this setting, test your form and site to be sure it supports PHP sessions. PHP Sessions are no longer enabled by default allowing for best compatibility with servers, caching, themes, and other plugins. This should resolve many sessions related issues some users had.
Let me know if it works.