xero api failing to add tracking on purchase order

Question

When I add tracking to invoices or credit notes via the api it works fine. but when i try to add it on purchase order it fails and I cannot seem to get a clear error message out of it.

I am using accounting api https://xeroapi.github.io/xero-php-oauth2/docs/v2/accounting/index.html#api-Accounting-updatePurchaseOrder

Error I get is message: "[400] Client error: POST https://api.xero.com/api.xro/2.0/PurchaseOrders/42797164-58c9-483c-9af8-96165c31a26f` resulted in a 400 Bad Request response:\n{\r\n "ErrorNumber": 10,\r\n "Type": "ValidationException",\r\n "Message": "A validation exception occurred",\r\n "Elements" (truncated...)\n" `

Code I am using to try set it after I have created the purchase order.

[$trackingCategoryId, $trackingOptionId] = $this->getTrackingCategoryByNameFromXero($projectName, 'Project');
        $purchaseOrder = null;

        $xeroTenantId = $this->xero_account->tenantId;

        try {
            $purchaseOrders = $this->accountingApi->getPurchaseOrder($xeroTenantId, $purchaseOrderId);
            foreach ($purchaseOrders as $model) {
                if ($model->getPurchaseOrderId() == $purchaseOrderId) {
                    $purchaseOrder = $model;
                    break;
                }
            }
        } catch (Exception $e) {
            echo 'Exception when calling AccountingApi->getPurchaseOrder: ', $e->getMessage(), PHP_EOL;
        }

        if ($purchaseOrder instanceof PurchaseOrder) {
            $lineItems = $purchaseOrder->getLineItems();
            foreach ($lineItems as $lineItem) {
                $tc = new LineItemTracking();
                $tc->setTrackingCategoryId($trackingCategoryId);
                $tc->setTrackingOptionId($trackingOptionId);

                $lineItem->setTracking([$tc]);
                $lineItems[] = $lineItem;
            }
            $purchaseOrder->setLineItems($lineItems);

            $purchaseOrders = new PurchaseOrders();
            $arr_purchase_orders[] = $purchaseOrder;
            $purchaseOrders->setPurchaseOrders($arr_purchase_orders);
            $summarizeErrors = true;
            try {
                $x =  $this->accountingApi->updatePurchaseOrder(
                    $this->xero_account->tenantId,
                    $purchaseOrderId,
                    $purchaseOrders
                );
            } catch (\ApiException $e) {
                print_r($e->getMessage());die;
            }
        }