Okay, I think I am getting nearer… it seems it is to do with creating a nonce – a unique WP generated code to stop spammers from accessing the form. So in my functions.php, I have entered the call:
wp_nonce_field( 'new-reply_'.$topic_id );
which has created in my HTML:
<input type="hidden" id="_wpnonce" name="_wpnonce" value="31279b1d8f" />
<input type="hidden" name="_wp_http_referer" value="/" />
I think I’m warm, but it still doesn’t work… can anyone give me the final little detail to make it work…?