Problem Adding New Columns

Hi, I’ve tried many variables and I can’t get this to work. I’m using this snippet:

add_filter( 'shortcode_atts_wpcf7', 'custom_shortcode_atts_wpcf7_filter', 10, 3 );
 
function custom_shortcode_atts_wpcf7_filter( $out, $pairs, $atts ) {
  $my_attr = 'book-title';
 
  if ( isset( $atts[$my_attr] ) ) {
    $out[$my_attr] = $atts[$my_attr];
  }
 
  return $out;
}

with [text book-title default:shortcode_attr] and this in Additional settings: flamingo_book_title: "[book-title]" – plus trying flamingo_text, flamingo_book-title – and nothing’s showing up.

Form is – [contact-form-7 id="1912" title="form test" book-title="test"]