Same cURL script works in dev. Can't figure ou

Question

This is the script, working on my dev machine:

$certPath = SITE_ROOT.'/certs/GoDaddyRootCertificateAuthority-G2.crt';
$options = [
    CURLOPT_POST => 1,
    CURLOPT_URL => 'https://uat.dwolla.com/oauth/rest/offsitegateway/checkouts',
    CURLOPT_RETURNTRANSFER => 1,
    CURLOPT_POSTFIELDS => json_encode(['name'=>'value']),
    CURLOPT_HTTPHEADER => ['Content-Type: application/json'],
    CURLOPT_SSL_VERIFYPEER => true,
    CURLOPT_CAINFO => $certPath,
];
$ch = curl_init();

curl_setopt_array($ch, $options);
if( ! $result = curl_exec($ch)) $err = curl_error($ch);
curl_close($ch);

if(!$result) echo $err;
else print_r(json_decode($result,true));

echo '<br/><br/>';
readfile($certPath); //output cert on screen
echo '<br/><br/>';

No issues. Once I move it to my production environment, the cURL connection fails with this error:

SSL certificate problem: unable to get local issuer certificate

• The same .crt contents are printed, so I know the path to the certificate is not the problem.
• Both environments use PHP 5.6.23 on Apache 2.4
• Dev machine is Win 7 x64, prod machine is Linux CentOS 7

I don't know where to start looking for the cause. Why is the script not working in production?

UPDATE: Thanks to @blackpen's great tip in comments, I learned about the CURLOPT_VERBOSE option used to generate a log of the connection. Here is the output in the broken production environment:

• Hostname was NOT found in DNS cache
• Trying 104.20.47.245...
• Connected to uat.dwolla.com (104.20.47.245) port 443 (#0)
• successfully set certificate verify locations:
• CAfile: /path/to/GoDaddyRootCertificateAuthority-G2.crt CApath: none
• SSL certificate problem: unable to get local issuer certificate
• Closing connection 0

Here is the log from the same script, but from the working development environment:

• Hostname in DNS cache was stale, zapped
• Trying 104.20.48.245...
• Connected to uat.dwolla.com (104.20.48.245) port 443 (#0)
• Cipher selection: ALL:!EXPORT:!EXPORT40:!EXPORT56:!aNULL:!LOW:!RC4:@STRENGTH
• successfully set certificate verify locations:
• CAfile: /path/to/GoDaddyRootCertificateAuthority-G2.crt
  CApath: none
• NPN, negotiated HTTP1.1
• SSL connection using TLSv1.2 / ECDHE-RSA-AES128-GCM-SHA256
• Server certificate:
• ...(cert details)
• SSL certificate verify ok.
• ... (more POST details)

Answer 1

I was able to get the script to work in both environments by replacing the .crt that worked only in the dev environments with a file named cacert.pem taken from here

I still don't know what exactly was going on but I suspect that it may have something to do with the formatting of the certificate. Perhaps PHP on Windows could deal with the .crt, but PHP on Linux couldn't. I got the idea from the highest rated answer on another question.