How to get all custom fields list using API?

How to get all custom fields list using API (With/Without specific module)?

I have tried get all custom fields using

https://www.zoho.com/crm/help/api/getfields.html

But its returns only the default fields for each module

Example:
Try to get custom fields from lead module

https://crm.zoho.com/crm/private/json/Leads/getFields?authtoken=<AUTH_TOKEN>&scope=crmapi&type=1

Result:
{"Leads":{"section":[{"dv":"Lead Information","FL":[{"dv":"Lead Owner","customfield":"false","maxlength":"120","isreadonly":"false","label":"Lead Owner","type":"Lookup","req":"false"},{"dv":"Company","customfield":"false","maxlength":"100","isreadonly":"false","label":"Company","type":"Text","req":"true"},{"dv":"Last Name","customfield":"false","maxlength":"80","isreadonly":"false","label":"Last Name","type":"Text","req":"true"},{"dv":"Email","customfield":"false","maxlength":"100","isreadonly":"false","label":"Email","type":"Email","req":"false"},{"dv":"Phone","customfield":"false","maxlength":"30","isreadonly":"false","label":"Phone","type":"Phone","req":"false"},{"dv":"Mobile","customfield":"false","maxlength":"30","isreadonly":"false","label":"Mobile","type":"Phone","req":"false"},{"val":["-None-","Attempted to Contact","Contact in Future","Contacted","Junk Lead","Lost Lead","Not Contacted","Pre-Qualified"],"dv":"Lead Status","customfield":"false","maxlength":"120","isreadonly":"false","label":"Lead Status","type":"Pick List","req":"false"}],"name":"Lead Information"},{"dv":"Description Information","name":"Description Information"},{"dv":"Address Information","name":"Address Information"},{"dv":"Visit Summary","name":"Visit Summary"}]}}

The above result doesn't contain the custom fields.

Thanks in advance.