Sectigo/Comodo SSL Root Certificate Expiring May 30, 2020
AddTrust External CA Root that was used to sign Sectigo Certificates expired on May 30, 2020.
Since you acquired a Sectigo/Comodo Positive SSL Certificate the statement above might be true for you.
Read more about it here: https://www.ssls.com/knowledgebase/sectigo-root-certificate-expiring-may-30-2020/
You don’t need to do anything if your website doesn’t use any web applications. When a web application connects to your website via SSL by itself, for example, a payment gateway app that gets server responses about the payment status. (PayPal will not show any errors).
However, if your website does use web applications then you may see errors in the apps and you have to reinstall the CA Bundle. To do it, follow this guide: https://www.ssls.com/knowledgebase/sectigo-root-certificate-expiring-may-30-2020/
We apologize for the inconvenience caused.
We are glad and ready to answer your questions.
If you have any questions, you can contact our support team. https://cleantalk.org/my/support/open