Let's Encrypt certificates are only valid for 3 months. but solutions exists to renew it automatically.
They had that but it seems to have stopped working. If they remember it's probably not much or an issue to just keep manually renewing it every three months.
There is another solution: cheap SSL certificates costing less then 10 USD and expiration time is a year or more.
Let's Encrypt is OK, but admin needs to check his site, sometimes.
But I don't really care about SSL expiration, it's over 24 hours since I'm waiting for my Bitcoin ("chips")