NSURLSession/NSURLConnection HTTP load failed

Hello,
I'm working on a new mobile application used to monitor sales on Envato Markets. I'm having a problem with the last update to iOS9.

When application tries to connect to envato API I'm getting an error:

NSURLSession/NSURLConnection HTTP load failed (kCFStreamErrorDomainSSL, -9802)

I'm trying to add this line in my config.xml file:

<key>NSAppTransportSecurity</key>
<dict>
  <key>NSAllowsArbitraryLoads</key>
  <true/>
</dict>

but still getting an error.

Are you familiar with this issue?
Can anybody suggest a solution?

Thank you.

Regards,
Krzysiek