API serves as a way to file lawsuit. It is humans who process them. This court deals with standard claims like businesses not paying for the service/goods but also consumers not paying their bills.

API is useful for companies like mobile operators or utility providers who have thousands of subscribers who do not pay.

1.6M payment orders, 21 months, 200 staff = ~17 cases per day per person (no holidays and vacations). Sounds doable given it is likely to be batches of claims as described above.