Add new text checkout field

Here is an example of how to add an additional text field ‘new_field’ into the checkout form:

add_filter('babe_checkout_args', 'customtheme_babe_checkout_args', 10, 2);
/**
 * Add checkout text field
 */
function customtheme_babe_checkout_args( $args_meta, $args ) {
    $args_meta['new_field'] = $args['meta']['new_field'] ?? '';
    return $args_meta;
}
////////
add_filter('babe_checkout_field_label', 'customtheme_babe_checkout_field_label', 10, 2);
/**
 * Add checkout field title
 */
function customtheme_babe_checkout_field_label( $field_title, $field_name ) {
    if ($field_name === 'new_field'){
       $field_title = __('Field Title', 'textdomain');
    }
    return $field_title;
}
////////
add_filter('babe_checkout_field_required', 'customtheme_babe_checkout_field_required', 10, 2);
/**
 * Required tag for checkout field. Use it only if you need to make field required
*/
function customtheme_babe_checkout_field_required($required_tag, $field_name){
   if ($field_name === 'new_field'){
      $required_tag = 'required="required"';
   }
   return $required_tag;
}
///////////////////
add_filter('babe_sanitize_checkout_vars', 'customtheme_sanitize_checkout_vars', 10, 2);
/**
 * Add fields to sanitize checkout vars method
 */
function customtheme_sanitize_checkout_vars( $output, $arr ) {

    $output['new_field'] = isset($arr['new_field']) ? sanitize_text_field($arr['new_field']) : '';
    return $output;
}

Add another field types: radio, checkbox and select

The next snippet can be used as an example for custom radio, checkbox and select fields:

function customtheme_get_hotels(){
    return [
        'hotel1' => __('Hotel name 1', 'textdomain'),
        'hotel2' => __('Hotel name 2', 'textdomain'),
        'hotel3' => __('Hotel name 3', 'textdomain'),
        'hotel4' => __('Hotel name 4', 'textdomain'),
        'hotel5' => __('Hotel name 5', 'textdomain'),
    ];
}

function customtheme_get_radios(){
    return [
        'radio1' => __('Radio value 1', 'textdomain'),
        'radio2' => __('Radio value 2', 'textdomain'),
    ];
}

add_filter('babe_checkout_field_label', 'customtheme_babe_checkout_field_label', 10, 2);
function customtheme_babe_checkout_field_label( $field_title, $field_name ) {

    if ( $field_name === 'checkbox' ){
        $field_title = __( 'Checkbox title', 'textdomain' );
    }
    if ( $field_name === 'radio' ){
        $field_title = __( 'Radio title', 'textdomain' );
    }
    if ( $field_name === 'hotel' ){
        $field_title = __( 'Hotel', 'textdomain' );
    }

    return $field_title;
}

add_filter('babe_checkout_after_contact_fields', 'customtheme_add_fields', 10, 2);
function customtheme_add_fields( $output, $args ){

    $hotels = customtheme_get_hotels();
    $radios = customtheme_get_radios();

    $hotels_options = '<option value>'.__( 'Select...', 'textdomain' ).'</option>';
    $hotel = !empty($args['meta']['hotel']) ? $args['meta']['hotel'] : '';

    foreach( $hotels as $hotel_code => $hotel_name){
        $hotels_options .= '<option value="'.esc_attr($hotel_code).'" '.selected($hotel, $hotel_code,false).'>'.esc_html($hotel_name).'</option>';
    }

    $radio_value = !empty($args['meta']['radio']) ? $args['meta']['radio'] : '';

    $checkbox_value = !empty($args['meta']['checkbox']) ? 1 : 0;

    $output .= '<h3>'. __( 'Checkbox and Hotel', 'textdomain' ) .'</h3>';

    $output .= '<div class="address_fields_group input_group">
        <div class="checkout-form-block checkout_select_block">
          <div class="checkout_select_title">
             <div class="checkout_checkbox_wrapper checkout_form_input_field_content">
              <input type="checkbox" class="checkout_form_input_field_checkbox" name="checkbox" id="checkbox" value="1" '. checked($checkbox_value, 1, false) . ' > 
              <label for="checkbox">'. BABE_html::checkout_field_label('checkbox') .'</label>
             </div>
          </div>
       </div>
       
       <div class="checkout-form-block checkout_select_block">
          <div class="checkout_select_title">
             <div class="checkout_select_wrapper checkout_form_input_field_content">
              <label class="checkout_form_input_label">' . BABE_html::checkout_field_label('hotel') . '</label>
              <select class="checkout_select_field select2" name="hotel" id="hotel">'.$hotels_options.'</select>
             </div>
          </div>
       </div>
       
       <div class="checkout-form-block checkout_select_block">
          <div class="checkout_select_title">
             <div class="checkout_radio_wrapper checkout_form_input_field_content">
              <label class="checkout_form_input_label">' . BABE_html::checkout_field_label('radio') . '</label>';

    foreach( $radios as $radio_code => $radio_name){
        $radio_value = empty($radio_value) ? $radio_code : $radio_value;
        $output .= '<div class="checkout_form_input_field_radio_wrapper">
               <input type="radio" class="checkout_form_input_field_radio" id="'.sanitize_key($radio_code).'" name="radio" value="'.esc_attr($radio_code).'" '. checked($radio_value, $radio_code, false) . ' > 
              <label for="'.sanitize_key($radio_code).'">'. esc_html($radio_name) .'</label>
           </div>';
    }

    $output .= '
             </div>
          </div>
       </div>
       
     </div>';

    return $output;
}

add_filter('babe_sanitize_checkout_vars', 'customtheme_sanitize_checkout_vars', 10, 2);
function customtheme_sanitize_checkout_vars( $output, $arr ) {

    $hotels = customtheme_get_hotels();
    $radios = customtheme_get_radios();

    $output['checkbox'] = !empty($arr['checkbox']) ? 1 : 0;
    $output['radio'] = isset($arr['radio'], $radios[$arr['radio']]) ? $arr['radio'] : '';
    $output['hotel'] = isset($arr['hotel'], $hotels[$arr['hotel']]) ? $arr['hotel'] : '';
    return $output;
}

add_filter('babe_order_customer_details_fields', 'customtheme_customer_details_fields', 10, 2);
function customtheme_customer_details_fields($order_meta, $order_id){

    $order_meta['checkbox'] = !empty($order_meta['checkbox']) ? __( 'yes', 'textdomain' ) : __( 'no', 'textdomain' );

    $hotels = customtheme_get_hotels();
    if ( !empty($order_meta['hotel']) && isset($hotels[ $order_meta['hotel'] ]) ){
        $order_meta['hotel'] = $hotels[ $order_meta['hotel'] ];
    }

    $radios = customtheme_get_radios();
    if ( !empty($order_meta['radio']) && isset($radios[ $order_meta['radio'] ]) ){
        $order_meta['radio'] = $radios[ $order_meta['radio'] ];
    }

    return $order_meta;
}

add_action( 'cmb2_admin_init', 'customtheme_order_customer_extra_fields', 20, 1);
function customtheme_order_customer_extra_fields() {

    $hotels = customtheme_get_hotels();
    $radios = customtheme_get_radios();

    $cmb = new_cmb2_box( array(
        'id'            => 'order_customer_extra_fields',
        'title'         => __( 'Extra fields', 'textdomain' ),
        'object_types'  => array( BABE_Post_types::$order_post_type, ), // Post type
        'context'       => 'normal',
        'priority'      => 'high',
        'show_names'    => true,
    ) );

    $cmb->add_field( array(
        'name' => BABE_html::checkout_field_label('checkbox'),
        'id'   => 'checkbox',
        'type'    => 'checkbox',
    ) );

    $cmb->add_field( array(
        'name' => BABE_html::checkout_field_label('radio'),
        'id'   => 'radio',
        'type'    => 'radio',
        'options' => $radios,
    ) );

    $cmb->add_field( array(
        'name' => BABE_html::checkout_field_label('hotel'),
        'id'   => 'hotel',
        'type'    => 'select',
        'show_option_none' => true,
        'options' => $hotels,
    ) );
}