The current UI for creating payment schedules is tedious, slow and error prone.

Why should someone have to figure out what percentage equally splits an invoice over 12 months? and why must a specific date be set for each payment. I understand flexibility is useful, but setting up a 12 month payment plan shouldn't take 10 minutes of work with a customer waiting, just to find out you forgot to change the 'due date' so the payment schedule wont save and you have to start again.