Developer Docs

Follow those steps:

1. Go to your WordPress Dashboard
2. Edit your Main Theme or Child Theme -> function.php page
3. Then, paste the sample code below and update these files.

Note: You can run this code anywhere

Add recurring Payment Type

add_filter('cleanly/form_data/step2/payment/type', function( $types ){
    // code here
    $types['28'] = esc_html__( '28 Days', 'cleanly' );
    // end code here
    return $types;
});