Add additional content to Custom Field during indexing in SearchWP

searchwp-customizations.php

<?php

// Add additional content to Custom Field during indexing in SearchWP.
add_filter( 'searchwp\source\post\attributes\meta', function( $meta_value, $args ) {
  if ( 'my_custom_field_key' !== $args['meta_key'] ) {
    return $meta_value;
  }
  
  // Add 'coffee' to Custom Field value to make it searchable.
  return $meta_value[0] . ' coffee';
}, 20, 2 );