The domain must be checked annually.
For this, log in as RA operator at https://ra.swisssign.ch with the SwissID (see also the Note on RA Operators).
If the domain is new or not in the list, add it.
If the validation is pending or has expired, open the next menu via the Edit button.
If necessary, restart the check and enter the key as a TXT record in the DNS zone.
Without a successful domain check, the service URL rejects all requests with the error "bad request".
SwissSign Support can be reached at mpki@swisssign.com for further questions.