How to fix "Modulus Mismatch" error

That is quite a popular error appearing during SSL installation to your web server. The error means you were using a different pair of CSR code and Private Key during placing the SSL order, so basically you do not have the proper key for the SSL certificate issued by the Certificate Authority (CA).

A few words about theory, when you request an SSL certificate, you generate a pair of CSR (Certificate Signing Request) code and Private key. You provide CSR code to the certificate authority and they issue SSL for your private key. Only one private key will match the SSL.

The most common reasons why you may have the wrong key:

  • You have generated multiple CSR codes and do not remember which key is a proper one;
  • You have accidentally removed the RSA private key from your server;
  • Your hosting control panel, like Plesk or cPanel/WHM fetch and auto-fill the installation form with an old certificate or key. We suggest trying to paste the certificate and Private key manually to exclude possible issues.

The working solutions.

  • Try to check if your issued SSL matches the RSA key using our Online matcher. Retry the installation process if they do match.
  • Generate a new pair of CSR and RSA key and process the reissue of your certificate.
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