shopify REST Admin API Response header doesn’t includes a URL for the next page of results

According to the official shopify documentation , “https://shopify.dev/docs/api/usage/pagination-rest#make-a-request-for-paginated-data”
there will be a link to the next page in the response header , but in my practical scenario , theres no link available , am i missing somthing ?

there are almost 60 products in my store,
my first api call returns the exact number of product i set as $perPage value properly, but i can not find the value of “link” to get the URL for the next page of results.

Thanks in advance.

        $productEndpoint = "https://".$this->shop."/admin/api/2024-01/products.json";
        $perPage = 20; // Set the desired number of products per page
      
        
        $allProducts = [];
        
        do {
            // Append query parameters for per_page and page
            $url = $productEndpoint."?limit=".$perPage;
            
            $ch = curl_init($url);
            curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
            curl_setopt($ch, CURLOPT_HTTPHEADER, [
                'Content-Type: application/json',
                'X-Shopify-Access-Token: ' . $this->accessToken,
            ]);
        
            $response = curl_exec($ch);
            $headers  = curl_getinfo($ch);
          
           
            $productDataArray   = json_decode($response, true);
           echo "All Headers:n";
           var_dump($headers);
            
            // Close the cURL connection
            curl_close($ch);
        


        } while (true);