Unable to Verify the First Certificate
The server sends its own certificate but not the intermediate that links it to a trusted root. Browsers sometimes fill the gap; curl, Node.js and APIs do not. Check the site below to confirm what is wrong.
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SSL Certificate Checker
The error, and the fix
Error CodesUNABLE_TO_VERIFY_LEAF_SIGNATURE
Usual CauseThe server sends its own certificate but not the intermediate that links it to a trusted root
Check From a Terminalopenssl s_client -connect example.com:443 -servername example.com
The server sends its own certificate but not the intermediate that links it to a trusted root. Browsers sometimes fill the gap; curl, Node.js and APIs do not.
How to fix it: Configure the full chain: fullchain.pem with Let's Encrypt (not cert.pem), or append the CA's intermediate to your certificate file.
SSL Errors
Questions
What does "unable to verify the first certificate" mean?
The server sends its own certificate but not the intermediate that links it to a trusted root. Browsers sometimes fill the gap; curl, Node.js and APIs do not.
How do I fix it?
Configure the full chain: fullchain.pem with Let's Encrypt (not cert.pem), or append the CA's intermediate to your certificate file.
Is it safe to click through the warning?
Not on a site where you enter passwords or payment details: the connection may not be private. Fix the certificate instead.
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