How to generate a List key

I have any issue when I have to integrate my website with Zoho CRM. My website is developed in WordPress. The plugin is asking for a LIST KEY which I am unable to figure out.

I do not want to use ZOHO Web Forms.

Check this

https://www.zoho.com/campaigns/help/using-apis.html#List_Key

I am unable to view any "list Key" screen