stampdoor

Thank you for your reply.

I followed your advice and added a process for when the file field is empty and it works as desired.

add_filter('cf7_2_post_metafield_file', 'change_meta_field_file_format', 10, 6);
function change_meta_field_file_format( $file_format, $attachment_id, $post_id, $post_field, $form_field, $cf7_key ){

	if ( empty( $_FILES[$form_field]['name'] ) ) {
		return '';
	}
	
    $file_format = $attachment_id . '_' . $form_field;

    return $file_format;

}