wc_avatax_http_request_args.php

function sfire_avatax_http_request_args($args, $this) {

	$body = $args['body'];
	$body = json_decode($body);

	if(!empty($body->PurchaseOrderNo)) {

		if(!empty($body->DocCode)) {

			$body->DocCode = $body->PurchaseOrderNo;

			$body = json_encode( $body );

			$args['body'] = $body;
		}
	}

	return $args;

}
add_filter('wc_avatax_http_request_args', 'sfire_avatax_http_request_args', 10, 2);