$item_id_1 = 1234567890;
$item_id_2 = 0987654321;
$feedback = 'Thanks for a smooth transaction!';

$transaction_id_1 = 771234567819;
$transaction_id_2 = 770987654319;

$requestXmlBody = '<?xml version="1.0" encoding="utf-8" ?>';
$requestXmlBody .= '<CompleteSaleRequest xmlns="urn:ebay:apis:eBLBaseComponents">';

$requestXmlBody .= "<ItemID>$item_id_1</ItemID>";
$requestXmlBody .= "<ItemID>$item_id_2</ItemID>";

$requestXmlBody .= "<FeedbackInfo>";
$requestXmlBody .= "<CommentText>$feedback_text</CommentText>";
$requestXmlBody .= "<CommentType>Positive</CommentType>";
$requestXmlBody .= "</FeedbackInfo>";

$requestXmlBody .= "<Shipped>true</Shipped>";
$requestXmlBody .= "<TransactionID>$transaction_id_1</TransactionID>";
$requestXmlBody .= "<TransactionID>$transaction_id_2</TransactionID>";

$requestXmlBody .= "<RequesterCredentials><eBayAuthToken>$userToken</eBayAuthToken></RequesterCredentials>";
$requestXmlBody .= '</CompleteSaleRequest>';