If it is about an invoice you cannot send or figures that look wrong, say which screen and what you expected, because that is almost always enough to find it.
How long a reply takes
Without a subscription, three to five working days. With Koi Pro your mail is answered first: usually within one to two working days.
Both go to the same mailbox and the same person reads them, so there is no second queue and nothing is filtered out unanswered. Paying moves you up the one queue there is, and that is the whole of the difference.
Before you write
Getting your books off the phone
Settings › Import and export writes everything (invoices, clients, expenses, time, and your receipt photographs) to a single file you can email to yourself or keep. It reads back into a fresh install on any phone.
Signing in, and what an account is for
The app works entirely without one. An account keeps a copy of the books so that a lost phone does not lose them, and so a second device can pick them up. Signing out of a phone leaves the books on it.
Deleting your account
Settings › Account › Delete my account removes the cloud copy and your receipt photographs, and closes the account. It cannot be undone, and it does not touch the books on the phone in your hand. See Privacy › Leaving.
The receipt reader
Photographing a receipt always keeps the photograph, whether or not the figures are read off it for you. If the reader is unavailable, the scanner still files the picture and you type the total. Nothing is lost.