The "Invalid Service Level" error occurs when a request is submitted with an invalid need-by date (e.g. a date in the past). Since the service level is calculated based on the need-by date, an invalid date prevents DocFind from calculating the appropriate service level.
A request with this error appears as Idle / Check Manual with the error message in the Log Messages at the bottom of the screen.
To work on the request, action Request as usual and go to the Additional Service Details section to edit the need-by date and add the Service Level. In most cases, where the need-by date is in 4 days or more, the correct service level is "Normal-Local Search". If an item is needed sooner, use the "Priority-Local Search" service level instead.
After this and any other needed changes, scroll to the top of the request and change the Authorisation Status to "To be Authorised" before clicking Request. This will re-run Docfind so that the proper default settings (like expiry days) are associated with the request, and so that locations can be added automatically to the rota if a match is found.