The above or a similar message generally indicates that something on your computer or network is intercepting and possibly monitoring your connection to the Zotero servers. The Zotero SSL certificates should always be valid.

(If you're getting a certificate error for a proxy or WebDAV URL, that's a different issue.)

Try the following steps to debug the problem:

1. Restart Zotero and/or your computer and try syncing again. This error can be caused by intermittent network issues.
2. Make sure your system clock and time zone are set correctly.
3. If you get the same error after restarting, load https://api.zotero.org (or the URL from your error message, being sure to use 'https', not 'http') in your browser (e.g., Firefox, Chrome, Safari).
   • If you see the message “Nothing to see here”, continue to Step 4.
   • If your browser displays an SSL certificate warning, someone or something may be intercepting your web traffic. Do not whitelist the certificate, as zotero.org's certificate should not be invalid and you will no longer have any guarantee that your connection to zotero.org is secure. (Whitelisting the certificate in your browser will also have no effect on Zotero.) Talk to your network administrator or ISP.
4. If you see the message “Nothing to see here” after loading the URL in your browser but continue to get SSL certificate errors in Zotero, your sync requests may be getting intercepted, possibly due to malware or security software on your system or a proxy server on your network. The following steps may help you debug or fix the problem:
   • View the certificate information for zotero.org or the URL in question, which may show what is intercepting your connections.
   • Check your system for malware.
   • If you are using security software, try temporarily disabling it, or disable its SSL/TLS/HTTPS-scanning feature.
   • If you are using a laptop, try syncing from a different network.
   • If you are in an institutional environment, ask your network administrator if they have installed a “custom root certificate” in your browser. If so, you can try following the certificate override instructions for Zotero, but be aware that your connection to Zotero is being intercepted and possibly monitored.
   • In rare circumstances, reinstalling Zotero may help.