REST API - can't update snippets

Thanks for the reply.

Requests in Postman were fine, problem was it had to work in *some* backend language that would allow me to fetch some structured data and update the Marketo snippet with the content.

There were two problems.

First, the cURL request didn't return correctly without CURLOPT_SSL_VERIFYPEER set to false, and second, I needed to urlencode() the content instead of adding slashes.

Here's my working function in PHP, in case it's of use to anyone else.

function updateSnippet($url, $access_token, $content, $type) {
    $ch = curl_init($url); // your Marketo API endpoint   
    curl_setopt($ch, CURLOPT_HTTPHEADER, array('accept: application/json'));
    curl_setopt($ch, CURLOPT_POST, true);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
    curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, FALSE);
    curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 2);
    curl_setopt($ch, CURLOPT_POSTFIELDS, "access_token=".$access_token."&type=".$type."&content=".urlencode($content));
    curl_getinfo($ch);
    $response = curl_exec($ch);
    return $response;
}
$snippet_id = 99;
$url = "https://xxx-yyy-zzz.mktorest.com/rest/asset/v1/snippet/".$snippet_id."/content.json";
$content = "The new snippet content goes here!";
$type = "HTML";
// $access_token = your Marketo REST API access token
$response = updateSnippet($url, $access_token, $content, $type);
var_dump($response);