I'm the CTO of a company tackling exactly this problem (www.salesbricks.com) and I'd go one further.
The complexity in billing, invoicing, payments etc are _not_ the stuff that computers or systems do. The complexity is and always will be in the stuff humans do.
The complexity in billing, invoicing, payments etc are _not_ the stuff that computers or systems do. The complexity is and always will be in the stuff humans do.