WooCommerce Checkout: Add multiple custom fields to billing area - customer case

functions.php

// Initial inspiration: https://businessbloomer.com/woocommerce-add-shipping-phone-checkout/
// My Custom Fields 
// Can be added to billing, shipping or order area. For the account page use the word account.
add_filter( 'woocommerce_checkout_fields', 'custom_fields_checkout' );
function custom_fields_checkout( $fields ) {
	
   $fields['billing']['billing_idrettslag'] = array(
      'label' => 'Hvilken idrettslag/ forening/ klasse?',
      'type'  => 'text',
      'required' => true,
      'class' => array( 'form-row-wide' ),
      'priority' => 28,
   );
	
    $fields['billing']['billing_antall'] = array(
      'label' => 'Antall personer som skal selge',
      'type'  => 'text',
      'required' => true,
      'class' => array( 'form-row-wide' ),
      'priority' => 29,
   );
	
    $fields['billing']['billing_kontakt'] = array(
      'label' => 'Kontaktperson hos Celias',
      'type'  => 'select',
      'required' => true,
      'class' => array( 'form-row-wide' ),
      'priority' => 75,
      'options'  	=> array( // options for <select> or <input type="radio" />
	      ''    		=> 'Velg', // empty values means that field is not selected 
                                      // 'value'=>'Name'
		            	'Ingen kontakt person'	=> 'Ingen kontakt person', 
			            'Regine'	              => 'Regine',
			            'Mei Mei'	              => 'Mei Mei'
		  )
		);

   $fields['order']['billing_nyhetsbrev'] = array(
      'label' => 'Jeg vil motta nyhetsbrev fra Celias.no',
      'type'  => 'select',
      'required' => true,
      'class' => array( 'form-row-wide' ),
      'priority' => 29,
      'options'  	=> array( // options for <select> or <input type="radio" />
	      ''    					=> 'Velg', // empty values means that field is not selected 
                                      // 'value'=>'Name'
		            					'Ja'	=> 'Ja', 
			            				'Nei'   => 'Nei',
			            
		  )
		);
	
  
	// Added below the order notes area.
    $fields['order']['billing_alder'] = array(
      'label' => 'Jeg er over 18.',
      'type'  => 'checkbox',
      'required' => true,
      'class' => array( 'form-row-wide' ),
      'priority' => 28,     
   );
		
   return $fields;	
	
}



// https://stackoverflow.com/questions/12958193/show-custom-field-on-order-in-woocommerce
// Custom fields that were added to the Order area will here be shown in the Billing area inside the WP backend WooCommerce -> Order and "Order Details" page.
add_action('woocommerce_checkout_update_order_meta','my_custom_checkout_field_update_order_meta');
function my_custom_checkout_field_update_order_meta($order_id) {
  if (!empty($_POST['billing']['billing_alder'])) {
     update_post_meta($order_id, 'Jeg er over 18', esc_attr($_POST['billing']['billing_alder2']));
     }
  if (!empty($_POST['billing']['billing_nyhetsbrev'])) {
     update_post_meta($order_id, 'Jeg vil motta nyhetsbrev fra Celias.no?', esc_attr($_POST['billing']['billing_nyhetsbrev2']));
     }	
 }


 // Display custom fields in the backend Order details screen.       
add_action( 'woocommerce_admin_order_data_after_billing_address', 'customfields_billing_checkbox_checkout_display' );
function customfields_billing_checkbox_checkout_display( $order ){
  echo '<p><b>Hvilken idrettslag/ forening/ klasse?</b> '  . get_post_meta( $order->get_id(), '_billing_idrettslag', true ) . '</p>';
	echo '<p><b>Antall personer som skal selge:</b> '      . get_post_meta( $order->get_id(), '_billing_antall', true ) . '</p>';
	echo '<p><b>Kontaktperson hos Celias?</b> '  . get_post_meta( $order->get_id(), '_billing_kontakt', true ) . '</p>';
	echo '<p><b>Nyhetsbrev:</b> '      . get_post_meta( $order->get_id(), '_billing_nyhetsbrev', true ) . '</p>';
	echo '<p><b>Jeg er over 18:</b> ' . get_post_meta( $order->get_id(), '_billing_alder', true ) . '</p>';
}

// Display custom fields in the admin and customer e-mails.
/* -------- E-mail custom fields ------ */

add_action( 'woocommerce_email_header', 'ts_email_header', 10, 2 );
function ts_email_header( $email_heading, $email ) { 
	echo "<p> Thanks for shopping with us. Here is your invoice </p>";
}

add_action( 'woocommerce_email_order_details', 'ts_email_order_details', 10, 4 );
function ts_email_order_details( $order, $sent_to_admin, $plain_text, $email ) {
	echo '<p>Hey '.$order->get_billing_first_name().', We hope you had fun shopping with us.';
}

add_action( 'woocommerce_email_before_order_table', 'ts_email_before_order_table', 10, 4 );
function ts_email_before_order_table( $order, $sent_to_admin, $plain_text, $email ) {
	echo "We hope to see you soon";
}

add_action( 'woocommerce_email_after_order_table', 'ts_email_after_order_table', 10, 4 );
function ts_email_after_order_table( $order, $sent_to_admin, $plain_text, $email ) {
	echo '<h2>"Additional information"</h2>';
	echo '<p><strong>'.__('Hvilken idrettslag/ forening/ klasse?').':</strong> <br/>' . get_post_meta( $order->get_id(), '_billing_idrettslag', true ) . '</p>';
        echo '<p><strong>'.__('Antall personer som skal selge').':</strong> <br/>' . get_post_meta( $order->get_id(), '_billing_antall', true ) . '</p>';
	echo '<p><strong>'.__('Kontaktperson hos Celias').':</strong> <br/>' . get_post_meta( $order->get_id(), '_billing_kontakt', true ) . '</p>';
	echo '<p><strong>'.__('Jeg vil motta nyhetsbrev fra Celias.no').':</strong> <br/>' . get_post_meta( $order->get_id(), '_billing_nyhetsbrev', true ) . '</p>';
	echo '<p><strong>'.__('Jeg er over 18.').':</strong> <br/>' . get_post_meta( $order->get_id(), '_billing_alder', true ) . '</p>';
}

add_action( 'woocommerce_email_customer_details', 'ts_email_customer_details', 10 , 4);
function ts_email_customer_details($order, $sent_to_admin, $plain_text, $email){
	echo '<p>Your order is sent to the following address</p>';
}