unit_tag missing postID

Hi,

I build a small function to dynamically change the subject or the recipient, which used to work, but suddenly it doesn’t.
I tested everything and what I found is the unit_tag I use to get the postID didn’t contain the postID. It now lokks like this wpcf7-f13028-o1.

My code:

function customFormRecipient($contactForm){
    $submission = WPCF7_Submission::get_instance();  
  
    if($submission)  {  
        $unit_tag = $submission->get_meta( 'unit_tag' );  
        $explode_unit_tag = explode("-", $unit_tag);  
  
		// We're on the viewing request form  
		$postID = str_replace("p", "", $explode_unit_tag[2]);  

		//... We now have the postID. Go forth and conquer  
		
		$altSubject = get_post_meta($postID, 'alt_subject_form_box', true);
		
		$altRecipient = get_post_meta($postID, 'alt_recipient_form_box', true);

		// Get the submited form email data.
		$mailData = $contactForm->prop('mail');
		
		if ($postID){
		    if ($altSubject){
			  // Set the subject
			  $mailData['subject'] =  $altSubject;
			} 
			if ($altRecipient){
			  // Set the recipient
			  $mailData['recipient'] =  $altRecipient;
			} 
			
		} 			
		// Update/set the form properties.
		$contactForm->set_properties(['mail' => $mailData]);
	}  
}

add_action('wpcf7_before_send_mail', 'customFormRecipient');

Can anybody tell me what’s wrong and what I could change to retrieve the postID?

Thanks.