LE's original CA root cert expired a few months ago https://letsencrypt.org/docs/dst-root-ca-x3-expiration-september-2021/ https://letsencrypt.org/docs/dst-roo

LE's original CA root cert expired a few months ago https://letsencrypt.org/docs/dst-root-ca-x3-expiration-september-2021/ https://letsencrypt.org/docs/dst-root-ca-x3-expiration-septe... under some conditions older devices that have not been updated neither accept the expired root CA, nor have a copy of the replacement cert. You should ask the user about his system, when he last updated it etc.