Please see:
- Error Issuing certificate
- Problem accessing domain
- https://github.com/WebThingsIO/gateway/issues/2948
There is currently a problem with the gateway generating certificates due to a change made by Lets Encrypt. A fix has now landed in the source code, but has not yet made it into an over-the-air update.
I’m afraid there’s no easy way to manually renew the certificate that I’m aware of at the moment.