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."
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."