Hi,
You do not have to pass this in the input validation field. You need to pass this code ( ${import_objects("file_id","collection_name", ",", "true/false")} ) in the design tab of your CAPI inside the "input variable".
As per screenshot it seems that you are not using double quotes as well while passing the file id and collection name.
Note: It is recommended to use "read only" while using collection for security purpose.
Hope this will help you. Feel free to ask.
Thanks & Regards,
Shobhit
Fujitsu- RunMyProcess