Adding New Line to Sublist Locations is not Allowed
The error occurs when the Location sublist field isn't mapped.
To fix it, make sure you map the Location sublist when updating fields that can be changed per location. When importing Preferred Stock Level, Quantity on Hand, or Reorder Point, map the Location sublist (it’s a keyed sublist with a key icon). You can use internal ID, external ID, or location name for the Location field.