Partial payment invoicing

Partial payment invoicing

Greetings

I have questions related to payments and retainer invoices:

1. When I want to issue a partial payment invoice, I can't specify the portion to be paid or already paid, then balance to be shown as Due. 


2. Retainer invoice is only available as an option when Sales Order is created but then I can't issue it (having the details shown as per SO automatically). Also, if I want to issue it manually, I need to fill everything. 

In both situations (Purchase or Sales) there is no way to prepare partial payment from customers nor partial payment to vendors, where balance to be shown as Receivables and Payables. 

Could you please help in locating such process


Best Regards, 
Majed 
INPROSU