Free events (price_per_ticket=0) fail at checkout — LNbits rejects amountless invoices #17

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opened 2026-05-23 21:54:44 +00:00 by padreug · 0 comments

padreug commented

2026-05-23 21:54:44 +00:00

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Problem

When an organizer creates an event with price_per_ticket = 0, the buy
flow still routes through create_payment_request to generate a
bolt11 invoice. LNbits doesn't support amountless invoices, so the
request fails and the buyer never gets a ticket.

This affects both single-ticket and multi-ticket purchases (multi
just multiplies 0 × N = 0, so same failure).

Proposed fix

When unit_price * quantity == 0 after promo application, skip the
invoice flow entirely:

Don't call create_payment_request.
Generate a synthetic payment_hash (e.g. urlsafe_short_hash() —
stays consistent with the multi-ticket id scheme).
Create the N ticket rows with paid = True immediately, shared
payment_hash, distinct short-hash ids.
Inline-run the set_ticket_paid counter update + Nostr republish
for each row (or batch them through the same per-event lock).
Send notifications (send_ticket_notification_in_background) the
same way the invoice-paid path does.
Return TicketPaymentRequest with payment_request = None,
is_fiat = False, and the populated ticket_ids so the webapp
knows it's a paid-no-payment ticket and jumps straight to the
success screen.

Companion webapp work (`aiolabs/webapp`, `app:activities`)

The buy dialog should detect price_per_ticket * quantity == 0 and:

Relabel the CTA "Get free ticket" / "Get N free tickets".
After backend returns the ticket_ids without a payment_request,
skip the invoice-display screen and go directly to the success
modal.

Out of scope

Free-and-fiat events (allow_fiat=true, price=0) — meaningless;
same skip-invoice path applies. No special handling needed.
Promo codes that bring price to 0 — same code path; the promo
discount is applied before the unit_price * quantity == 0 check
so this works automatically.

Test plan

Create event with price_per_ticket = 0. Buy 1 → ticket lands
paid in My Tickets, no invoice, no wallet charge.
Buy 5 free → 5 rows, all paid, shared synthetic payment_hash.
event.sold += 5, amount_tickets -= 5. Nostr event republished
with new counters.
Event with price=100, promo code -100% → same flow, treats as
free.
Capacity check still rejects overbooking on free events.

## Problem When an organizer creates an event with `price_per_ticket = 0`, the buy flow still routes through `create_payment_request` to generate a bolt11 invoice. LNbits doesn't support amountless invoices, so the request fails and the buyer never gets a ticket. This affects both single-ticket and multi-ticket purchases (multi just multiplies 0 × N = 0, so same failure). ## Proposed fix When `unit_price * quantity == 0` after promo application, **skip the invoice flow entirely**: 1. Don't call `create_payment_request`. 2. Generate a synthetic `payment_hash` (e.g. `urlsafe_short_hash()` — stays consistent with the multi-ticket id scheme). 3. Create the N ticket rows with `paid = True` immediately, shared `payment_hash`, distinct short-hash ids. 4. Inline-run the `set_ticket_paid` counter update + Nostr republish for each row (or batch them through the same per-event lock). 5. Send notifications (`send_ticket_notification_in_background`) the same way the invoice-paid path does. 6. Return `TicketPaymentRequest` with `payment_request = None`, `is_fiat = False`, and the populated `ticket_ids` so the webapp knows it's a paid-no-payment ticket and jumps straight to the success screen. ## Companion webapp work (`aiolabs/webapp`, `app:activities`) The buy dialog should detect `price_per_ticket * quantity == 0` and: - Relabel the CTA "Get free ticket" / "Get N free tickets". - After backend returns the ticket_ids without a `payment_request`, skip the invoice-display screen and go directly to the success modal. ## Out of scope - Free-and-fiat events (allow_fiat=true, price=0) — meaningless; same skip-invoice path applies. No special handling needed. - Promo codes that bring price to 0 — same code path; the promo discount is applied before the `unit_price * quantity == 0` check so this works automatically. ## Test plan - [ ] Create event with `price_per_ticket = 0`. Buy 1 → ticket lands paid in My Tickets, no invoice, no wallet charge. - [ ] Buy 5 free → 5 rows, all paid, shared synthetic payment_hash. `event.sold += 5`, `amount_tickets -= 5`. Nostr event republished with new counters. - [ ] Event with price=100, promo code -100% → same flow, treats as free. - [ ] Capacity check still rejects overbooking on free events.

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aiolabs/events#17

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