The delivery threshold
Once a day the plugin adds up the net turnover from distance sales to private customers in the EU - per destination country and EU-wide, for the current and the previous calendar year, the way the €10,000 rule counts. While OSS is off, it warns from 90% of the limit on the tenant, on the dashboard and on the export page; an earlier warning can be set, but that does not move the legal limit. Once the limit is crossed with OSS still off, the check report of every export carries it as a finding too.
Without OSS
If OSS is off on the tenant, a sale to private customers in the EU with the German rate books like a domestic sale. If the order instead carries a rate Germany does not have, such as 21% to the Netherlands, it does not match the setting: the document stops and names country and rate. Until it is cleared up, the run writes no file.