The Web2Cit-Monitor uses the Web2Cit-Server's translate endpoint to get results (actual and expected outputs) for all template and test paths.
However, if no valid templates or tests are found, there are no paths to return results for.
In these cases the Web2Cit-Server is returning an overall "No targets" error, as documented in the Server documentation.
This may be undesired, because the Web2Cit-Monitor doesn't know how to handle this and returns an error for that domain.
Consider having the server return an empty array of results instead of an error in these cases, at least for the JSON response format. Note that for the HTML response format returning an error (instead of the translation summary page) may not be preferred either, as it would prevent users from easily editing the configuration files (once T319072 is resolved).