When you only have 10 users, the easiest ways to please all your users is to do things by hand that make the experience of those users excellent, rather than worrying about creating systems that will only pay off when you have 100,000 users.

When reddit started out and had almost no user base, they had employees each impersonate a handful of different users to give the site a sense of a pre-existing community. When Dwarf Fortress was starting out, their sole developer would create custom ASCII-art scenes to send to every supporter above a certain dollar threshold.

It means doing things that you can do when you have 0 to a few users but that would not work beyond that. For example, Doordash validated their idea with posters and manually taking orders and delivering them themselves, no app, no drivers.

It is counterintuitive at first but when you think about it actually makes a lot of sense. When you're getting started you should focus on doing things to get started. Worry about scaling when you're scaling.

Sending out invoices for example.

You can work on automating it and hooking various payment providers.

Integration with payment providers is a lot of hassle and engineering work. So when you have 5-10 customers it does not make sense to automate that.

Sending invoices manually does not scale of course - but that advice is given in specific context of company. Where you should focus on working on your product and not on automating invoices "because somewhere in the future it will be needed."

Premature optimization is the root of all evil.