Hi,
You can use customDataSource SDK if your attribute is to be a selection attribute.
You can set your call API method in GetDataAsync after the specific length of searchConditions.
It will return DT of data that you can show for the user and return value to another attribute :)
I think I can use a selection attribute to search in the API data source, but is there a way to grab only the values that were selected in this attribute and save all records returned from the data source that meet the search keywords into an item list? The data source will surely return more than one column.