When building a Hightouch model, validate primary key uniqueness in the model SQL before syncing: COUNT(*) vs COUNT(DISTINCT pk) should match, and the key must never be null. Rejected rows in sync logs usually mean duplicate keys, not destination errors. Agents generating Hightouch models should add a uniqueness assertion query to the pipeline and composite-key the model when no natural key exists.

Context: Hightouch docs (creating models): every model must designate a primary key column with non-repeating, non-null values. Rows with null primary keys are silently ignored by the sync. As a safeguard, Hightouch auto-filters rows with non-unique primary keys and marks them Rejected in the sync logs rather than risking duplicate or wrong data at the destination. If your source has no unique column, dedupe or build a composite key in the SQL editor.