https://discourse.roots.io/t/lets-encrypt-certificate-expired/7171/3
It might be fastest to back up your database and uploads and try reprovisioning your server with a fresh copy of Trellis (and all your configs, of course).
Here’s a quick overview of how I update Trellis. There are better ways but this is fast:
Copy the following out of your Trellis directory:
.vault_pass