I am writing to request urgent assistance with a license activation issue affecting all websites hosted on our server. We are unable to activate or validate site keys, and the process fails with the following detailed error:
cURL error 35: OpenSSL SSL_connect: SSL_ERROR_ZERO_RETURN in connection to api.wpml.org:443
We have conducted a thorough investigation with our hosting provider (Hostcreators.sk). Their engineers have confirmed that:
Outgoing traffic is clear: There are no restrictions on our server's firewall for outgoing connections to port 443.
IP-specific failure: The activation works perfectly when tested from different infrastructures (different IPs), but fails consistently from our server's IP range.
Handshake failure: The SSL_ERROR_ZERO_RETURN indicates that your server is terminating the connection during the SSL handshake, which strongly suggests an IP-based block at the firewall or CDN level (e.g., Cloudflare or similar) on your side.
Please check if the following IP addresses are blacklisted or blocked in your system and whitelist them:
This issue is preventing us from updating our plugins and launching new client projects and also translating on existing sites. We would appreciate it if you could escalate this to your systems administration or security team.
Thank you for your prompt attention to this matter.
I’m Prosenjit from the WPML Development Team, and I’ll be happy to assist you with this issue.
From the error you shared, it appears to be a TLS/SSL handshake failure. This type of error is usually caused by factors such as outdated OpenSSL libraries, incompatible SSL/TLS protocols, or firewall/proxy restrictions blocking the connection. Please note that WPML servers do not block individual IP addresses, so the issue is most likely related to the server environment or connection setup.
Since you mentioned that these aspects were already checked and seem to be working correctly, the next step would be to review the plugin setup. Based on the WPML Debug Information, I noticed that the WPML plugins and their add-ons currently installed on your site are quite outdated.
Over time, we have released multiple updates to improve compatibility, stability, and connectivity with WPML services. Because of this, I recommend updating WPML and all its add-ons to their latest versions and then checking whether the issue still occurs when activating the license.
If the updates are not available directly from the Plugins page, you can install them manually by following these steps:
- Log in to your WPML.org account
- Go to the Downloads section
- Download the latest versions of WPML and the required add-ons
- Upload and install them on your site
After updating the plugins, please clear both your site cache and browser cache, and then try activating the site key again.
Please try these steps and let me know how it goes. I’ll be happy to assist further if needed.
