I've played with the platform the past days. It's awesome and fits my needs. But, of course, there are a few things that would be great to have.
Generate PDF as receipt after a payment has been made.
I've actually amended the code and created this by myself because i really need to generate and send receipts after payments are made. I've cloned the default template for invoice, but removed some fields and added additional fields.
I've also added a custom field for payments table (receipt number) but because i'm not familiar with CI at all I have to add the receipt numbers manually (not fun!). If you like to amend this as a feature to IP let me know and i can send an archive with the modified/added files (not using Git :/). I guess you have my email address so just drop me a line.
An option to define an existing balance for a client would be great.
For example, i'm using IP for the year 2015 but of course i have invoices issued in 2014 using a different platform. Ideally would be to assign a starting balance for the clients that i have so when i register a payment made in 2015 (ref an invoice from 2014) it can state "against balance" and not really being "forced" to add the invoice from 2014 in the system. Hope you understand the case.
Other than these, I have other features in mind, but i'll suggest them as i go by.