Why do I keep getting unsupported_grant_type when using oAuth2 and curl?
This is not how to add POST data to cURL. There is PHP documentation to tell you what these options actually mean. Try this instead:
<?php$postdata = [ "client_secret"=>"xxx", "client_id"=>"xxx", "grant_type"=>"client_credentials", "scope"=>"delivery",];$cl = curl_init("https://login.uber.com/oauth/v2/token");curl_setopt_array($cl, [ CURLOPT_POST => true, CURLOPT_POSTFIELDS => $postdata, CURLOPT_RETURNTRANSFER => true]);$content = curl_exec($cl);curl_close($cl);var_dump($content);