Problem with "External Id" field when importing test cases to Jira using Zephyr Squad

I'm trying to import test cases from Excel to Jira cloud using Zephyr Squad, in the import process I Mhave a required field "External Id" and I mapped it to the ID column in my excel file (ex:TB-1). I want to use this field to reference the old ID of the testcase and maintain a compatibility with previous doc. 

My config .json file (it seems "External id"=id) :

The import is successful except that I can't see the field "External Id" anywhere and the value mapped to this field isn't visible anywhere. Can anyone plz help me figure out what is going on?