Since Let’s Encrypt is a free SSL certificate from the non-profit Internet Security Research Group (ISRG), it may be incompatible with some browsers. To see the list of compatible and incompatible browsers, go to the Certificate Compatibility page of the Let’s Encrypt site.

Compatibility with browsers is determined by whether the browser supports SHA-2 certificates and has IdenTrust’s DST Root X3 in its trust store.

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