I have some problem when i try to read an xml from ro e-Factura sistem file with php, with this function: I have some problem when i try to read an xml from ro e-Factura sistem file with php, with this function:

function parseXMLFactura($path_xml) {
        if (!file_exists($path_xml)) {
            return [];
        }
    
        $xml = simplexml_load_file($path_xml, "SimpleXMLElement", LIBXML_NOCDATA);
        $xml->registerXPathNamespace('cbc', 'urn:oasis:names:specification:ubl:schema:xsd:CommonBasicComponents-2');
        $xml->registerXPathNamespace('cac', 'urn:oasis:names:specification:ubl:schema:xsd:CommonAggregateComponents-2');
    
        $documentType = (string)$xml->getName();
        $creditNoteTypeCode = (string)$xml->xpath('//cbc:CreditNoteTypeCode')[0];
        $lineType = 'cac:InvoiceLine';
    
        if ($documentType == 'CreditNote') {
            $lineType = 'cac:CreditNoteLine';
        }
    
        $products = [];
        
        foreach ($xml->xpath('//' . $lineType) as $line) {
            $product = [];
            $product['denumire'] = (string)$line->xpath('cac:Item/cbc:Name')[0];
            $product['cod_produs'] = (string)$line->xpath('cac:Item/cbc:Description')[0];
            if (empty($product['cod_produs'])) {
                $product['cod_produs'] = $product['denumire'];
            }
            $product['cantitate'] = (string)$line->xpath('cbc:InvoicedQuantity')[0];
            if (empty($product['cantitate'])) {
                $product['cantitate'] = (string)$line->xpath('cbc:CreditedQuantity')[0];
            }
            $product['pret_buc'] = (string)$line->xpath('cac:Price/cbc:PriceAmount')[0];
            $product['val_tva'] = (string)$line->xpath('cac:Item/cac:ClassifiedTaxCategory/cbc:Percent')[0];
            $product['pret_raft'] = '0';  // Valoare implicită, actualizată ulterior dacă e cazul
            $product['unitate_masura'] = (string)$line->xpath('cbc:InvoicedQuantity/@unitCode')[0];
            if (empty($product['unitate_masura'])) {
                $product['unitate_masura'] = (string)$line->xpath('cbc:CreditedQuantity/@unitCode')[0];
            }
    
            // Invert values for CreditNote with type code 381
            if ($documentType == 'CreditNote' && $creditNoteTypeCode == '381') {
                $product['cantitate'] = '-' . $product['cantitate'];
                //$product['pret_buc'] = '-' . $product['pret_buc'];
            }
    
            $products[] = $product;
    
            // Verificăm dacă există discounturi
            foreach ($line->xpath('cac:AllowanceCharge') as $allowanceCharge) {
                if ((string)$allowanceCharge->xpath('cbc:ChargeIndicator')[0] === 'false') {
                    $discount = [];
                    $discount['denumire'] = (string)$allowanceCharge->xpath('cbc:AllowanceChargeReason')[0];
                    $discount['cod_produs'] = $discount['denumire']; // Denumirea este folosită ca și cod produs pentru discount
                    $discount['cantitate'] = '-1';
                    $discount['pret_buc'] = (string)$allowanceCharge->xpath('cbc:Amount')[0];
                    $discount['val_tva'] = (string)$line->xpath('cac:Item/cac:ClassifiedTaxCategory/cbc:Percent')[0];
                    $discount['pret_raft'] = '0';
                    $discount['unitate_masura'] = '';
    
                    // Invert discount amount for CreditNote with type code 381
                    if ($documentType == 'CreditNote' && $creditNoteTypeCode == '381') {
                        $discount['pret_buc'] = '-' . $discount['pret_buc'];
                    }
    
                    $products[] = $discount;
                }
            }
        }
    
        return $products;
    }

i receive: Warning: SimpleXMLElement::xpath(): Undefined namespace prefix can someone help me to understand why ?
for some xml file work for another appeat error Warning: SimpleXMLElement::xpath(): Undefined namespace prefix