JSON not well formed error

Hello.

Can anyone tell me why I always get a JSON not well formed error with the following command?
I can not find the error.

zoho.books.createRecord("contacts", "12345",
{
"contact_name" : input.first_name,
"company_name" : input.account_name_company,
"contact_persons" : {

{
"salutation" : input.salutation,
"first_name" : input.first_name,
"last_name" : input.last_name,
"email" : input.email,
"phone" : input.phone,
"mobile" : input.mobile,
"is_primary_contact" : true
}

},
"billing_address" : {

"address" : input.mailing_street,
"city" : input.mailing_city,
"state" : input.mailing_state,
"zip" : input.mailing_zip,
("country") : input.mailing_country
},

"custom_fields" : {

{ "index" : 1, "value" : input.type_of_customer },
{ "index" : 2, "value" : "YES" },
{ "index" : 3, "value" : input.payment_plan_hidden },
{ "index" : 4, "value" : input.Referrer }
}

}
);

I always get the following error message:

{"message":"JSON is not well formed","code":1038}

Regards