Working solution assuming your on Windows using XAMPP:

XAMPP server

1. Similar for other environment
   • download and extract for cacert.pem here (a clean file format/data)

https://curl.haxx.se/docs/caextract.html

2. Put it here in the following directory.

C:\xampp\php\extras\ssl\cacert.pem

3. In your php.ini put this line in this section ("c:\xampp\php\php.ini"):

;;;;;;;;;;;;;;;;;;;;; php.ini Options  ;;;;;;;;;;;;;;;;;;;;;curl.cainfo = "C:\xampp\php\extras\ssl\cacert.pem"

4. Restart your webserver/apache

5. Problem solved!

(Reference: https://laracasts.com/discuss/channels/general-discussion/curl-error-60-ssl-certificate-problem-unable-to-get-local-issuer-certificate)

Attention Wamp/Wordpress/windows users. I had this issue for hours and not even the correct answer was doing it for me, because i was editing the wrong php.ini file because the question was answered to XAMPP and not for WAMP users, even though the question was for WAMP.

here's what i did

Download the certificate bundle.

Put it inside of C:\wamp64\bin\php\your php version\extras\ssl

Make sure the file mod_ssl.so is inside of C:\wamp64\bin\apache\apache(version)\modules

Enable mod_ssl in httpd.conf inside of Apache directory C:\wamp64\bin\apache\apache2.4.27\conf

Enable php_openssl.dll in php.ini. Be aware my problem was that I had two php.ini files and I need to do this in both of them. First one can be located inside of your WAMP taskbar icon here.

and the other one is located in C:\wamp64\bin\php\php(Version)

find the location for both of the php.ini files and find the line curl.cainfo = and give it a path like this

curl.cainfo = "C:\wamp64\bin\php\php(Version)\extras\ssl\cacert.pem"

Now save the files and restart your server and you should be good to go

If you are using PHP 5.6 with Guzzle, Guzzle has switched to using the PHP libraries autodetect for certificates rather than it's process (ref). PHP outlines the changes here.

Finding out Where PHP/Guzzle is Looking for Certificates

You can dump where PHP is looking using the following PHP command:

 var_dump(openssl_get_cert_locations());

Getting a Certificate Bundle

For OS X testing, you can use homebrew to install openssl brew install openssl and then use openssl.cafile=/usr/local/etc/openssl/cert.pem in your php.ini or Zend Server settings (under OpenSSL).

A certificate bundle is also available from curl/Mozilla on the curl website: https://curl.haxx.se/docs/caextract.html

Telling PHP Where the Certificates Are

Once you have a bundle, either place it where PHP is already looking (which you found out above) or update openssl.cafile in php.ini. (Generally, /etc/php.ini or /etc/php/7.0/cli/php.ini or /etc/php/php.ini on Unix.)