将bash curl转换为php curl时出现的问题

有人能帮我把bash-curl转换成php-curl吗？它显示了内部错误

api_key="d6b991ecexxxxxxxxxxxxxxfedc3"
app_key="d06d8c833xxxxxxxxxxxxxf3ccf4"

curl -POST \
    -d 'graph_json={"requests":[{"q":"avg:system.load.1{*}"}],"viz":"timeseries","events":[]}' \
    -d "timeframe=1_hour" \
    -d "size=medium" \
    -d "legend=yes" \
    "https://app.datadoghq.com/api/v1/graph/embed?api_key=${api_key}&application_key=${app_key}"

---

//由curl到PHP生成：

$ch = curl_init();

curl_setopt($ch, CURLOPT_URL, $_ENV["https://app.datadoghq.com/api/v1/graph/embed?api_key={api_key}&application_key={app_key}"]);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, "graph_json={\"requests\":[{\"q\":\"avg:system.load.1{*}\"}],\"viz\":\"timeseries\",\"events\":[]}&timeframe=1_hour&size=medium&legend=yes");
curl_setopt($ch, CURLOPT_POST, 1);

$headers = array();
$headers[] = "Content-Type: application/x-www-form-urlencoded";
curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);

$result = curl_exec($ch);
if (curl_errno($ch)) {
    echo 'Error:' . curl_error($ch);
}
curl_close ($ch);