Order_Id : SalesOrders.SO Number

Hi,Why I can retreive the good order id of a sale order inside my email template ?
I don't understand this value : ${SalesOrders.SO Number}

I would like to use this value to retreive informations of an order with the api :

https://crm.zoho.com/crm/private/json/SalesOrders/getRecordById?newFormat=1&apikey=KEY&ticket=TICKET&id=ORDER_ID

But it doesn't seems to be the good value...
Thanks