The full error message can look like this:

"Client error: `POST https://live.api.otto.market/v1/shipments` resulted in a `409 Conflict` response:
{\"errors\":[{\"title\":\"POSITION_ITEM_INCLUDED_IN_OTHER_SHIPMENT\",\"detail\":\"One or more of the given position item ids alre (truncated...)

This usually means that the position of the order (PositionItemID) has already been reported (manually directly at OTTO Market in the OPC).
We cannot consider manual shipping notifications.