HDL - update position on asg error

Summary

HDL - update position on asg - parent record not found

Content

Im trying to update a position on an employees assignment but keep getting "A parent for this record was not found. Use any of the four supported key-resolution systems to supply a valid parent reference." below is the metadata. Do i need the original source keys when the assignment was created (where do i get these from) or can i supply my own like below, or maybe i need the right ids or other columns ?

METADATA|WorkTerms|SourceSystemOwner|SourceSystemId|ActionCode|ReasonCode|EffectiveStartDate|EffectiveEndDate|EffectiveSequence|EffectiveLatestChange|PrimaryWorkTermsFlag|PersonNumber|AssignmentNumber