Answer
A plain generic Insert/Update-from-File Migration Job procedure isn't the right mechanism for custom-field data specifically — the correct built-in flow is a two-step process: first load the raw source data into a staging table via the file import, then use the framework's dedicated 'Migrate Source Data' procedure, specifically designed for populating custom fields from that staged data, following IFS's documented 'Migrate data into Custom Fields' guidance rather than a plain generic insert/update job. Separately, if the Excel Add-in migration path is being attempted instead and the job won't execute or start at all, this commonly indicates the Excel Add-in's own separate license simply isn't part of the environment's current entitlement — in that case, fall back to the traditional Migration Job plus Source Data procedure described above rather than the Excel-based path.