“Please enter a valid postcode/ZIP.”Error for some customers

Hello,

You can disable postcode validation by adding the following code:

add_filter( 'woocommerce_checkout_fields' , 'bbloomer_alternative_override_postcode_validation' );
 
function bbloomer_alternative_override_postcode_validation( $fields ) {
$fields['billing']['billing_postcode']['required'] = false;
$fields['shipping']['shipping_postcode']['required'] = false;
return $fields;
}

(resource: https://www.businessbloomer.com/woocommerce-disable-postcodezip-validation-checkout/)

I would recommend using a plugin like Code Snippets to add the snippet to your site.