Let's encrypt certificate is cross signed with IdenTrust, which is widely known, but if you've got an old platform it can fail for other reasons like missing su

Let's encrypt certificate is cross signed with IdenTrust, which is widely known, but if you've got an old platform it can fail for other reasons like missing support for SHA2. See this page for details: https://letsencrypt.org/docs/certificate-compatibility/ https://letsencrypt.org/docs/certificate-compatibility/