Wordpress Invoice Plugin Adaptation

I am using Sprout Invoices. When credits are applied to the balance, the balance doesn't reflect the credit. It just shows $0. I need the balances to show the correct credit balance, so you need to have an understanding of Accounting as well as Wordpress. PLEASE DO NOT APPLY FOR THIS JOB IF YOU ARE UNSURE IF YOU CAN DO IT! I cannot afford to waste my time on people who assure me they can do it but then can't. Sprout Invoices say it should take 30 - 60 minutes, but they are not available until next week. I am on a time crunch and need this done NOW. I understand that it may take another hour or more for you to familiarize yourself with the plugin, but total should not be more than max 3 or 4 hours. Note: If your bid says complete in 2 or more days it will be rejected. I need this done today. Note: I am a woman. If you refer to me as Sir or Mate, your bid will be trashed immediately since you have obviously not read or understood my job post. There are other less important changes I would like to make following this job, so please include your hourly rate in your bid. Thank you.