How do you close an invoice in Zoho CRM

How do you close an invoice in Zoho CRM

Hi there,
 
I am new to Zoho.  I have Zoho CRM and Zoho Invoice.  We are a sales driven industry and we create sales orders for our services.  Once the service is complete we convert the sales order into an invoice. 
 
The problem I have is that an invoice in the CRM does not transfer to Zoho Invoice.  I do not understand why they don't transfer because if you have an invoice you need to track payment for it etc.  The invoice needs to be tied to the sales order. The solution I was given was to create the invoice in Zoho Invoice, but that is a duplication of work.
 
If we create an invoice in Zoho CRM, how do we close the invoice?  How do we close out sales orders?
 
I can make a custom field with a status but the invoices and sales orders always appear.  This makes no sense to me as any company creating a sales order or an invoice needs to be able to close them.  Otherwise you will have pages and pages of sales orders and invoices. 
 
If you have a company that sells a products and you create sales orders, how do you use the CRM?  How do you close sales orders?  How do you close invoices?