Who builds Invoice Koi
Invoice Koi is an invoicing app for one- and two-person trades, built and run by Fang, a software ventures company registered in Singapore. Fang builds and operates its own software rather than building it for other people, which is the part that matters to anyone deciding whether to put a year of their invoices into this: the people who wrote it are the people who will still be answering the support address next year.
An invoice written where the job was done.
Invoicing software is mostly built for businesses with an office, and it shows in the assumptions: that there is a desk to come back to, a connection to rely on, and somebody whose job is the paperwork. A self-employed electrician has none of the three. The invoice gets written in a van, or at ten at night, or three weeks late because the evening it was supposed to happen was spent on a callout.
So the whole of Invoice Koi runs on the phone. The document is drawn there, the totals are worked out there, and the PDF is rendered there. Nothing waits on a server to answer, which is why it works in a plant room with no bars, and it is why there is no account to make before the first invoice: the app has nothing to sync until you decide it should.
Four rules, and they are Fang's.
Fang publishes how it builds, and Invoice Koi is built that way rather than in spite of it. Start from a problem someone already has, and not a market it would be nice to be in. Ship where the work happens: the phone in the van, not the browser at the desk that trade does not sit at. Keep the team small enough that a decision is a conversation. And claim only what the code does.
That last one is the reason the comparison pages list what the other eleven apps do better, and the reason a feature the vendor does not name on their own pricing page is scored as not stated rather than counted in our favour. It is also why this page has no founding story on it. There is one, and it has not been written down anywhere a reader could check, so it is not here yet.
Three things, stated plainly.
It does not email your clients. The share sheet opens with the PDF on it and you press send, from your own address, so the invoice arrives from the person who did the work rather than from software they have never heard of. It does not detect payments, either: you record them, because a bank feed this app does not have would be a guess dressed as a fact.
And it does not hold your books hostage. Everything exports as CSV, spreadsheet or PDF, and the backup file is yours to keep. An invoicing app that is hard to leave is an invoicing app that has stopped competing for the people already in it.
One address, read by the people who build it.
Support is support@invoicekoi.com, and it reaches the people who wrote the thing you are asking about. Anything about partnerships or distribution is better sent to Fang directly at wj@fangv.xyz. Fang's other product is Intriq, which is relationship memory for the web and iPhone, and is unrelated to invoicing except in being built the same way.