Client Payment
Yes. Whenever you update /add customer payment in invoice. Your customer will receive cash receipt along with invoice copy on their email ID (which is mentioned while creating invoice).
Yes. You can update the payment on multiple divident basis like advance payment, installment 2, installment 3 & etc..
Yes. Travel CEO will send an automated balance reminder for your customer. You (Your admin) can customise the email content in Email Notification settings page.