Hi @thanhtonyc,

I think you’re getting this error because the parameter is not set into the request correctly.

You can refer to the following sample code to call the PDF to ZPL API with PHP:

<?php
function CallAPI($width, $height, $filename) {
    $curl = curl_init();
    curl_setopt($curl, CURLOPT_POST, 1);
    curl_setopt($curl, CURLOPT_URL, "https://html-to-zpl.p.rapidapi.com/pdf2zpl");
    curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1);
    curl_setopt($curl, CURLOPT_FOLLOWLOCATION, 1);
    curl_setopt($curl, CURLOPT_MAXREDIRS, 10);
    curl_setopt($curl, CURLOPT_TIMEOUT, 30);

    curl_setopt($curl, CURLOPT_HTTPHEADER, [
        "X-RapidAPI-Host: html-to-zpl.p.rapidapi.com",
        "X-RapidAPI-Key: YOUR_API_KEY",
        "content-type: application/json"
    ]);

    $pdfRaw = file_get_contents($filename);
    $pdfBase64 = base64_encode($pdfRaw);

    $data = [
        "width" => $width,
        "height" => $height,
        "pdfBase64" => $pdfBase64
    ];
    curl_setopt($curl, CURLOPT_POSTFIELDS, json_encode($data));

    $result = curl_exec($curl);

    curl_close($curl);

    return $result;
}

$zpl = CallAPI(4, 6, "test.pdf");
echo $zpl;

(replace YOUR_API_KEY with your own key from RapidAPI)

I just tested this here, and it works well.

Please let me know if this works for you, or if you need more code samples!