Add a custom field (in an order) to the emails

wc-add-custom-field.php

/**
 * Add a custom field (in an order) to the emails
 */
add_filter( 'woocommerce_email_order_meta_fields', 'custom_woocommerce_email_order_meta_fields', 10, 3 );

function custom_woocommerce_email_order_meta_fields( $fields, $sent_to_admin, $order ) {
    $fields['meta_key'] = array(
        'label' => __( 'Label' ),
        'value' => get_post_meta( $order->id, 'meta_key', true ),
    );
    return $fields;
}

@marketingsolution I have a snippet in my tutorial: https://www.kathyisawesome.com/woocommerce-customize-checkout-fields/

This should display fields on the woocommerce_email_customer_details hook. You can check the email templates for available hooks.

function kia_display_email_order_meta( $order, $sent_to_admin, $plain_text ) { 
	$some_field = $order->get_meta( '_some_field' ); 
	$another_field = $order->get_meta( '_another_field' ); 
	if( $plain_text ){ 
		echo 'The value for some field is ' . $some_field . ' while the value of another field is ' . $another_field;
	} else { 
		echo 'The value for <strong>some field</strong> is ' . $some_field. ' while the value of <strong>another field</strong> is ' . $another_field . ';
	} 
} 
add_action('woocommerce_email_customer_details', 'kia_display_email_order_meta', 30, 3 );

Thank you I dont know for what we are using this else { } ?
I try to adapt it but've got critical error on page, please take a look, want to show just one field txt:
`function NIP_display_email_order_meta( $order, $sent_to_admin, $plain_text ) {
$NIP = $order->get_meta( '_NIP' );

if( $plain_text ){ 
	echo 'Podany NIP to ' . $NIP;
} else { 
	echo 'The value for <strong>some field</strong> is ' . $NIP.;
} 

}
add_action('woocommerce_email_customer_details', 'NIP_display_email_order_meta', 30, 3 );
`

@marketingsolution the if/else is for emails that are sent in plain text versus emails that are sent with HTML markup. You didn't say what your fatal error was so it's hard to say... though I do see a problem at the end of echo 'The value for <strong>some field</strong> is ' . $NIP.; there's a period just before the semi-colon that should not be there.

function NIP_display_email_order_meta( $order, $sent_to_admin, $plain_text ) {
  $NIP = $order->get_meta( '_NIP' );
  
  if( $plain_text ){ 
	  echo 'Podany NIP to ' . $NIP;
  } else { 
	  echo 'The value for <strong>some field</strong> is ' . $NIP;
  } 

}
add_action('woocommerce_email_customer_details', 'NIP_display_email_order_meta', 30, 3 );