Nudgebook, I created to remind freelancers about their invoices. Three mistakes during first 6 weeks

Background info: Nudgebook is a service that sends polite reminders to freelancers who hate chasing payments. I created Nudgebook after once having to wait 74 days for a payment from a client whom I liked, but was too embarrassed to follow up. Rather than just announcing it, I want to share my mistakes with you.

Mistake one: I created the reminder system before the onboarding process. Users would sign up, not connect anything, and leave. Changing the invoice import to the first screen increased the number of people reaching an active reminder by twofold.

Mistake two: my default email tone was too friendly. Test users said they would ignore such an email. When I re-wrote the third reminder to be concise yet polite, the response time from real clients decreased dramatically.

The third mistake was charging on an invoice basis. This was because freelancers have fluctuating months, and a sudden increase in charges made them uncomfortable. I changed to a fixed monthly charge, and the issues were sorted.

I am still very new, and I understand my product is flawed in some ways. I would appreciate any feedback from freelance people regarding what they would like my tool to do when chasing unpaid bills. Would they like to send the message, draft the message, or just find out who is overdue?