Unable to get contacts from account, ZohoCRM

Unable to get contacts from account, ZohoCRM

I have created admin CRM account and able to get AUTHTOKEN using Zoho Book API as follows:

#
#Tue Sep 29 07:36:43 PDT 2015
AUTHTOKEN=b11c78429e9f0334f5e831c6781xxxxx
RESULT=TRUE

but when I try to access Contact from this account I got following response using API GET request
I got following response
{
    "code": 6024,
    "message": "This user belongs to multiple organizations, hence the parameter organization_id is required for associating this user to a specific organization.",
    "error_info": []
}

so for that I tried to access the organization for the user using the API GET request
" https://books.zoho.com/api/v3/organizations?authtoken=b11c78429e9f0334f5e831c6781xxxxx"
I got following response
{
    "code": 0,
    "message": "success",
    "organizations": []
}

why this is so? I am using this API for CRM admin and it has organization. this account has Contact in it.