Key fields must be top-level
Symptom I used a joiner to enrich one data stream with data from another. However, even though my key fields were at the top of their respective column list, I have got the error "key fields must be top-level". Cause Not identically named fields as key fields. Solution Make sure, you name join attributes/fields identically. It is matching over names. Remark The error message is somewhat misleading as it was just unable to find matching attribute independently from the position, the were at.