Issuing

You pass the billable items you picked, a client, and your invoice reference. The items are read, frozen onto an invoice, and marked as invoiced so they cannot land on a second one.

⛔⛔ AN INVOICE IS A DOCUMENT, NOT A LIVE VIEW. The lines are copied onto the record at issue time and never recomputed. If an item is edited afterwards this invoice does not move, because you already sent it. Restating a number a client is holding is a discrepancy, not a correction.

⛔ AN ITEM ALREADY ON AN INVOICE IS REFUSED. Every picked item must still be pending; one that is not halts the whole run rather than quietly dropping out, because a silently shorter invoice is money you never bill and never notice.

⚠ The invoice carries the currency; items do not. An amount typed into a GBP invoice is GBP. If you are passing on something you bought in another currency, convert it when you record the item — the rate you used and the day you used it are your decision, and a pack that guessed one would be wrong in a way you could not see.

⛔ Items carry money, so nothing is priced here. A rate belongs where hours become items (pull-billable-hours) or where you typed the figure (add-billable-item). An invoice adds up decisions already made.

⛔⛔ VAT IS RECORDED, NEVER COMPUTED. You give the figure; the pack stores it and adds it to the net. It does not know a rate, a scheme, a registration status or a place of supply, and it will never derive one — a pack that got tax 95% right would be more dangerous than one that never claimed to.

⚠ Two ways to carry VAT, and you should pick one. Either give vat_amount here — the invoice then shows net, VAT and total separately, which is what a client expects to see — or put VAT in as an ordinary billable item and leave this at 0. Do both and you have charged it twice; the invoice will show a VAT line AND a VAT total, so it is visible rather than silent, but it is still wrong.

⚠ net is simply the sum of the lines. If you carried VAT as a line item then net includes it and is misnamed — the TOTAL is right either way, which is the number that matters to the person paying.

⚠ It does not send anything. No email, no payment provider, no reminder.

Credits, and the one thing an invoice cannot be

A negative billable item — a voucher, a discount — comes off the total like any other line. Nothing here treats it specially, and that is deliberate.

⛔ The total must be greater than zero. Not the lines — the document. Credits that cancel or exceed the charges make something this pack cannot express: an invoice that says we owe you. It would issue as open with nothing to collect, sit in your open list forever, and never settle, because record-payment reduces an outstanding balance and there is no negative one to reduce. Refusing at issue is the only point where that is still a typo rather than a stuck record.