WordPress at a glance
function is not described

wc_paying_customer() WC 1.0

Order payment completed - This is a paying customer.

No Hooks.

Return

null. Nothing.

Usage

wc_paying_customer( $order_id );
$order_id(int) (required)
Order ID.

Code of wc_paying_customer() WC 5.2.2

<?php
function wc_paying_customer( $order_id ) {
	$order       = wc_get_order( $order_id );
	$customer_id = $order->get_customer_id();

	if ( $customer_id > 0 && 'shop_order_refund' !== $order->get_type() ) {
		$customer = new WC_Customer( $customer_id );

		if ( ! $customer->get_is_paying_customer() ) {
			$customer->set_is_paying_customer( true );
			$customer->save();
		}
	}
}