Answer
Check specifically whether the CONTRACT (Site) column has been defined in the migration job template — even when every other mandatory (flagged 'M') field has a template mapping or default value, a missing CONTRACT/Site mapping specifically produces this 'Unit code does not exist' error, since the site context is what the framework uses to resolve and validate the unit code against. Reviewing the full list of mandatory fields (marked with 'M' in the Flag column) and ensuring each has either a template column mapping or a default value — with particular attention to CONTRACT — resolves this.