Email Attachments not working

Hi, I’ve tried to add an attachment to response email with the following code:

function filter_ninja_forms_action_email_attachments( $attachments, $data, $settings ) { 
         
         if ($data['form_id'] == 2) {

             $attachments[] = "wp-content/uploads/2017/11/filename.pdf";
             return $attachments;
         }
         return $attachments; 
     }; 
              
     // add the filter 
     add_filter( 'ninja_forms_action_email_attachments', 'filter_ninja_forms_action_email_attachments', 10, 3 );

But it isn’t working. Via WP Mail Log I can see the attachment appended to the outgoing email, but I don’t receive it on the destination email address.

Could you kindly help?