Yup, this was a lesson I learned the hard way when I built out billing for our SaaS product. I had spent weeks thinking about user accounts, team accounts, subscription, integration with Stripe, how the UI would look, how I would verify VAT numbers for European customers, etc etc etc. In the end I threw all the code away because not a single customer that we had would have used self-checkout billing anyway, everything happens via email, purchase orders, billing portals like Ariba, etc. Monthly subscriptions are far and few between, pay-per-use is something that almost no customer would be interested in. Some customers actually wanted multi-year subscriptions, which Stripe doesn't even support.

It's emails and spreadsheets all the way down if you're building a product for an Enterprise audience.