curl vs libcurl command using php-curl - php

Question

I have a curl command that works perfectly from the command line that goes like so :
curl --cert /path/to/cert.pem \
--cert-type PEM \
--form "files[0]=#/path/to/file.csv" \
https://url.com/whatever
I can also run it successfully from php using
exec("curl --cert /path/to/cert.pem --cert-type PEM --form \"files[0]=#/path/to/file.csv\" https://url.com/whatever");
Translating the command to php-curl I got
$url = "https://url.com/whatever";
$certificate = "/path/to/cert.pem";
$filePath = "/path/to/file.csv";
$postData = array("files[0]" => "#".$filePath);
// Upload request
$ch = curl_init($url);
curl_setopt($ch, CURLOPT_SSLCERT, $certificate);
curl_setopt($ch, CURLOPT_SSLCERTTYPE, "PEM");
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, $postData);
// I have tried WITH or WITHOUT the following options to no avail
// Note that SSL_VERIFYPEER false is not necessary -- I do not have a self-signed cert in the chain
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 2);
$postUploadResponse = curl_exec($ch);
and this does not work. The message I get from the server is that the authentication has failed and that my certificate is not valid (though the exact same certificate works from the cmd line).
An important detail : that function runs perfectly well (with SSL_VERIFYPEER false as I use a self-signed cert locally) from my local XAMPP installation but the same code fails on the server.
The server is on Debian 8.3.
curl --version is
curl 7.38.0 (x86_64-pc-linux-gnu) libcurl/7.38.0 OpenSSL/1.0.1k zlib/1.2.8 libidn/1.29 libssh2/1.4.3 librtmp/2.3
Protocols: dict file ftp ftps gopher http https imap imaps ldap ldaps pop3 pop3s rtmp rtsp scp sftp smtp smtps telnet tftp
Features: AsynchDNS IDN IPv6 Largefile GSS-API SPNEGO NTLM NTLM_WB SSL libz TLS-SRP
What could be causing this ? Is there anything that could be causing my certificate to not be sent properly when using libcurl ?