Invalid items
Show invalid items appears an option if any of the records in your dataset are not valid (according to the rules of the schema chosen for the mapping) after transformation. This is usually because a small number of items in the original dataset lack information in one or two elements. Click on Show invalid items to see the list of problematic records and then click on an item record.
Reviewing invalid items
On the right-hand side at the top of the panel there is an option to Show/hide report, clicking on the shows a list of the validation errors in this item record.
Reviewing invalid item report
Reviewing the invalid items allows you to assess whether adjusting the mapping could improve the results. There may be data in the original dataset that was excluded from the transformation, perhaps because it was missed in the mapping or filtered out by a condition. In such cases you can return to the original mapping, edit the mapping, and run the transformation again.
Note: You may decide that although some records are invalidated as the majority have transformed well to go ahead with publication. Remember that you can process an update of your dataset later once new data becomes available (on your native system) to validate the missing records.