diff --git a/src/modules/events/lib/promoCodes.spec.ts b/src/modules/events/lib/promoCodes.spec.ts
new file mode 100644
index 0000000..8369c3f
--- /dev/null
+++ b/src/modules/events/lib/promoCodes.spec.ts
@@ -0,0 +1,93 @@
+import { describe, expect, it } from 'vitest'
+import {
+  applyPercent,
+  fromWirePromoCodes,
+  hasPromoErrors,
+  isUnsupportedEndpointError,
+  normalizePromoCode,
+  toWirePromoCodes,
+  validatePromoRows,
+  type PromoCodeRow,
+} from './promoCodes'
+
+function row(overrides: Partial<PromoCodeRow> = {}): PromoCodeRow {
+  return { code: 'HALF', discount_percent: 50, max_uses: null, active: true, ...overrides }
+}
+
+describe('normalizePromoCode', () => {
+  it('trims and upper-cases, and tolerates null', () => {
+    expect(normalizePromoCode('  summer24 ')).toBe('SUMMER24')
+    expect(normalizePromoCode(null)).toBe('')
+    expect(normalizePromoCode(undefined)).toBe('')
+  })
+})
+
+describe('validatePromoRows', () => {
+  it('accepts a well-formed row', () => {
+    const errors = validatePromoRows([row()])
+    expect(errors).toEqual([{}])
+    expect(hasPromoErrors(errors)).toBe(false)
+  })
+
+  it('flags an empty code', () => {
+    expect(validatePromoRows([row({ code: '  ' })])[0].code).toBe('events.create.promo.errors.required')
+  })
+
+  it('flags duplicates case-insensitively on both rows', () => {
+    const errors = validatePromoRows([row({ code: 'half' }), row({ code: ' HALF ' })])
+    expect(errors[0].code).toBe('events.create.promo.errors.duplicate')
+    expect(errors[1].code).toBe('events.create.promo.errors.duplicate')
+    expect(hasPromoErrors(errors)).toBe(true)
+  })
+
+  it('requires the percentage to be within 1..100', () => {
+    for (const pct of [null, 0, 101, Number.NaN]) {
+      expect(validatePromoRows([row({ discount_percent: pct })])[0].discount_percent)
+        .toBe('events.create.promo.errors.percentRange')
+    }
+    expect(validatePromoRows([row({ discount_percent: 100 })])[0].discount_percent).toBeUndefined()
+  })
+
+  it('allows blank max uses and rejects zero / fractions', () => {
+    expect(validatePromoRows([row({ max_uses: null })])[0].max_uses).toBeUndefined()
+    expect(validatePromoRows([row({ max_uses: 3 })])[0].max_uses).toBeUndefined()
+    expect(validatePromoRows([row({ max_uses: 0 })])[0].max_uses).toBe('events.create.promo.errors.maxUsesMin')
+    expect(validatePromoRows([row({ max_uses: 1.5 })])[0].max_uses).toBe('events.create.promo.errors.maxUsesMin')
+  })
+})
+
+describe('toWirePromoCodes / fromWirePromoCodes', () => {
+  it('normalises codes, drops used_count and maps blank max uses to null', () => {
+    expect(toWirePromoCodes([row({ code: ' half ', used_count: 4 }), row({ code: 'CAP', max_uses: 2 })])).toEqual([
+      { code: 'HALF', discount_percent: 50, active: true, max_uses: null },
+      { code: 'CAP', discount_percent: 50, active: true, max_uses: 2 },
+    ])
+  })
+
+  it('round-trips the wire shape and tolerates the older three-field shape', () => {
+    expect(fromWirePromoCodes([{ code: 'OLD', discount_percent: 20, active: false }])).toEqual([
+      { code: 'OLD', discount_percent: 20, max_uses: null, active: false, used_count: 0 },
+    ])
+    expect(fromWirePromoCodes(undefined)).toEqual([])
+    expect(fromWirePromoCodes([{ code: 'CAP', discount_percent: 10, active: true, max_uses: 0, used_count: 2 }]))
+      .toEqual([{ code: 'CAP', discount_percent: 10, max_uses: null, active: true, used_count: 2 }])
+  })
+})
+
+describe('applyPercent', () => {
+  it('rounds sats down to whole units and fiat to two decimals', () => {
+    expect(applyPercent(333, 15, 'sat')).toBe(283)
+    expect(applyPercent(59.97, 33, 'EUR')).toBe(40.18)
+    expect(applyPercent(1000, 100, 'sats')).toBe(0)
+  })
+})
+
+describe('isUnsupportedEndpointError', () => {
+  it('recognises 404/405 and nothing else', () => {
+    expect(isUnsupportedEndpointError(Object.assign(new Error('x'), { status: 404 }))).toBe(true)
+    expect(isUnsupportedEndpointError(Object.assign(new Error('x'), { status: 405 }))).toBe(true)
+    expect(isUnsupportedEndpointError(Object.assign(new Error('x'), { status: 400 }))).toBe(false)
+    expect(isUnsupportedEndpointError(new Error('x'))).toBe(false)
+    expect(isUnsupportedEndpointError(null)).toBe(false)
+  })
+})
diff --git a/src/modules/events/lib/promoCodes.ts b/src/modules/events/lib/promoCodes.ts
new file mode 100644
index 0000000..812b62e
--- /dev/null
+++ b/src/modules/events/lib/promoCodes.ts
@@ -0,0 +1,125 @@
+import type { PromoCode } from '../types/ticket'
+
+/**
+ * Promo-code helpers shared by the organizer editor and the buyer
+ * dialog. Pure functions, no Vue — mirror `promo.py` in the events
+ * extension by name so the two sides stay recognisably in step:
+ *
+ *   normalizePromoCode  ↔  promo.normalize_code
+ *   applyPercent        ↔  promo.round_amount / basket_totals (display fallback only)
+ *
+ * The server's `POST /events/api/v1/promo/validate/{event_id}` is the
+ * source of truth for the discounted total; `applyPercent` exists so
+ * the UI can still show *something* against an older extension.
+ */
+
+/** One editor row. `discount_percent` / `max_uses` are `null` while the
+ *  organizer is still typing (empty inputs), never `0`-as-empty. */
+export interface PromoCodeRow {
+  code: string
+  discount_percent: number | null
+  /** `null` = unlimited (backend `max_uses: None`). */
+  max_uses: number | null
+  active: boolean
+  /** Derived by the backend from paid tickets; read-only in the editor. */
+  used_count?: number
+}
+
+/** Per-row validation messages as i18n keys (the component runs them
+ *  through `t()`); a missing field means the field is fine. */
+export interface PromoRowErrors {
+  code?: string
+  discount_percent?: string
+  max_uses?: string
+}
+
+const ERROR_KEYS = {
+  required: 'events.create.promo.errors.required',
+  duplicate: 'events.create.promo.errors.duplicate',
+  percentRange: 'events.create.promo.errors.percentRange',
+  maxUsesMin: 'events.create.promo.errors.maxUsesMin',
+} as const
+
+/** Trim + upper-case, the same normalisation the backend applies before
+ *  matching, so what the buyer sees in the input is what gets matched. */
+export function normalizePromoCode(raw: string | null | undefined): string {
+  return (raw ?? '').trim().toUpperCase()
+}
+
+/**
+ * Editor rules — stricter than the backend on purpose: the backend
+ * accepts 0 % (a no-op the buyer would see as "code not valid"), the
+ * editor requires 1–100 so an organizer cannot create a dud by accident.
+ */
+export function validatePromoRows(rows: PromoCodeRow[]): PromoRowErrors[] {
+  const seen = new Map<string, number>()
+  for (const row of rows) {
+    const code = normalizePromoCode(row.code)
+    if (code) seen.set(code, (seen.get(code) ?? 0) + 1)
+  }
+  return rows.map((row) => {
+    const errors: PromoRowErrors = {}
+    const code = normalizePromoCode(row.code)
+    if (!code) {
+      errors.code = ERROR_KEYS.required
+    } else if ((seen.get(code) ?? 0) > 1) {
+      errors.code = ERROR_KEYS.duplicate
+    }
+    const pct = row.discount_percent
+    if (pct === null || !Number.isFinite(pct) || pct < 1 || pct > 100) {
+      errors.discount_percent = ERROR_KEYS.percentRange
+    }
+    const max = row.max_uses
+    if (max !== null && (!Number.isInteger(max) || max < 1)) {
+      errors.max_uses = ERROR_KEYS.maxUsesMin
+    }
+    return errors
+  })
+}
+
+export function hasPromoErrors(errors: PromoRowErrors[]): boolean {
+  return errors.some((e) => Object.keys(e).length > 0)
+}
+
+/** Editor rows → wire `extra.promo_codes`. Drops the read-only
+ *  `used_count` (the backend recomputes it) and blank max-uses → `null`. */
+export function toWirePromoCodes(rows: PromoCodeRow[]): PromoCode[] {
+  return rows.map((row) => ({
+    code: normalizePromoCode(row.code),
+    discount_percent: row.discount_percent ?? 0,
+    active: row.active,
+    max_uses: row.max_uses && row.max_uses > 0 ? Math.trunc(row.max_uses) : null,
+  }))
+}
+
+/** Wire `extra.promo_codes` → editor rows. Tolerates the pre-`max_uses`
+ *  shape (older extension) and a missing list (public records). */
+export function fromWirePromoCodes(codes: PromoCode[] | null | undefined): PromoCodeRow[] {
+  return (codes ?? []).map((c) => ({
+    code: c.code,
+    discount_percent: c.discount_percent ?? 0,
+    max_uses: c.max_uses && c.max_uses > 0 ? c.max_uses : null,
+    active: c.active ?? true,
+    used_count: c.used_count ?? 0,
+  }))
+}
+
+/**
+ * Display-only fallback for the discounted total when the validate
+ * endpoint is unavailable. Rounds like the backend: whole sats, two
+ * decimals for fiat.
+ */
+export function applyPercent(subtotal: number, percent: number, currency: string): number {
+  const raw = subtotal * (1 - percent / 100)
+  const unit = currency.toLowerCase()
+  if (unit === 'sat' || unit === 'sats') return Math.max(0, Math.trunc(raw))
+  return Math.max(0, Math.round(raw * 100) / 100)
+}
+
+/** An older extension without the validate route answers 404 (or 405
+ *  when the path exists for another method). Anything else is a real
+ *  error. */
+export function isUnsupportedEndpointError(err: unknown): boolean {
+  const status = (err as { status?: unknown } | null)?.status
+  return status === 404 || status === 405
+}
diff --git a/src/modules/events/services/TicketApiService.spec.ts b/src/modules/events/services/TicketApiService.spec.ts
index 999ac80..3559f03 100644
--- a/src/modules/events/services/TicketApiService.spec.ts
+++ b/src/modules/events/services/TicketApiService.spec.ts
@@ -90,3 +90,57 @@ describe('TicketApiService.getTicket / resendTicketEmail', () => {
     expect(legacy.email).toEqual({ attempted: false, sent: false, error: null })
   })
 })
+
+describe('TicketApiService promo codes', () => {
+  const fetchMock = vi.fn()
+  let api: TicketApiService
+
+  beforeEach(() => {
+    fetchMock.mockReset()
+    vi.stubGlobal('fetch', fetchMock)
+    api = new TicketApiService({ baseUrl: BASE, apiKey: 'inst-key' })
+  })
+  afterEach(() => vi.unstubAllGlobals())
+
+  function lastCall() {
+    const [url, init] = fetchMock.mock.calls[0] as [string, RequestInit]
+    return { url, init, body: JSON.parse(init.body as string), headers: init.headers as Record<string, string> }
+  }
+
+  it('validatePromoCode posts the v2 shape with an upper-cased code', async () => {
+    const totals = {
+      subtotal: 2000, discount: 1000, total: 1000, currency: 'sat',
+      discounts_applied: [{ code: 'HALF', discount_percent: 50, discount_fixed: null, amount_saved: 1000 }],
+    }
+    fetchMock.mockResolvedValue(okJson(totals))
+    const res = await api.validatePromoCode('evt', ' half ', 2)
+    const { url, init, body } = lastCall()
+    expect(url).toBe(`${BASE}/events/api/v1/promo/validate/evt`)
+    expect(init.method).toBe('POST')
+    expect(body).toEqual({ codes: ['HALF'], quantity: 2 })
+    expect(res).toEqual(totals)
+  })
+
+  it('carries the HTTP status on errors so a missing route (older extension) is recognisable', async () => {
+    fetchMock.mockResolvedValue({ ok: false, status: 404, json: async () => ({ detail: 'Not Found' }) } as Response)
+    await expect(api.validatePromoCode('evt', 'HALF')).rejects.toMatchObject({ message: 'Not Found', status: 404 })
+  })
+
+  it('requestTicket forwards promo_code verbatim', async () => {
+    fetchMock.mockResolvedValue(okJson({ payment_hash: 'h', payment_request: 'lnbc1', is_fiat: false }))
+    await api.requestTicket('evt', { userId: 'u1', promoCode: 'HALF', quantity: 2 })
+    expect(lastCall().body).toEqual({ user_id: 'u1', promo_code: 'HALF', quantity: 2 })
+  })
+
+  it('createEvent sends extra.promo_codes verbatim', async () => {
+    fetchMock.mockResolvedValue(okJson({ id: 'evt' }))
+    const promo_codes = [{ code: 'HALF', discount_percent: 50, active: true, max_uses: 2 }]
+    await api.createEvent(
+      { name: 'E', event_start_date: '2030-01-01', extra: { promo_codes } },
+      'inkey',
+    )
+    const { body, headers } = lastCall()
+    expect(body.extra.promo_codes).toEqual(promo_codes)
+    expect(headers['X-API-KEY']).toBe('inkey')
+  })
+})
diff --git a/src/modules/events/services/TicketApiService.ts b/src/modules/events/services/TicketApiService.ts
index 9a2da22..2f8b291 100644
--- a/src/modules/events/services/TicketApiService.ts
+++ b/src/modules/events/services/TicketApiService.ts
@@ -1,4 +1,5 @@
 import type {
+  BasketTotals,
   EventTicket,
   EventTicketExtra,
   CreateTicketRequest,
@@ -9,7 +10,9 @@ import type {
   TicketResendResult,
   TicketedEvent,
   CreateEventRequest,
+  PromoValidateRequest,
 } from '../types/ticket'
+import { normalizePromoCode } from '../lib/promoCodes'
 
 export interface TicketApiConfig {
   baseUrl: string
@@ -335,6 +338,8 @@ export class TicketApiService {
       name?: string | null
       registered: boolean
       registered_at: string | null
+      /** Promo code the buyer redeemed (events ext >= v1.6.1-aio.12). */
+      applied_promo_code?: string | null
     }>
   }> {
     return this.request(`/events/api/v1/tickets/event/${eventId}/stats`, {
@@ -343,6 +348,22 @@ export class TicketApiService {
     })
   }
 
+  /**
+   * Preview what a promo code does to a purchase of `quantity` tickets
+   * (`POST /events/api/v1/promo/validate/{event_id}`, anonymous). The
+   * backend applies the first valid code; an empty `discounts_applied`
+   * means "not valid". Older extensions 404 — the thrown error carries
+   * `status` so callers can fall back to "applied at checkout".
+   */
+  async validatePromoCode(eventId: string, code: string, quantity = 1): Promise<BasketTotals> {
+    const body: PromoValidateRequest = { codes: [normalizePromoCode(code)], quantity }
+    return this.request(`/events/api/v1/promo/validate/${eventId}`, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify(body),
+    })
+  }
+
   /**
    * Mark a paid ticket as registered at the door. Organizer-only —
    * requires the event-owning wallet's admin_key. Backend rejects
@@ -441,7 +462,9 @@ export class TicketApiService {
         : Array.isArray(error.detail)
           ? error.detail[0]?.msg ?? 'Request failed'
           : 'Request failed'
-      throw new Error(errorMessage)
+      // Carry the HTTP status so callers can tell "route missing on an
+      // older extension" (404) apart from "bad input" (400).
+      throw Object.assign(new Error(errorMessage), { status: response.status })
     }
 
     return response.json()
diff --git a/src/modules/events/types/ticket.ts b/src/modules/events/types/ticket.ts
index d42b3c2c..67ee90f 100644
--- a/src/modules/events/types/ticket.ts
+++ b/src/modules/events/types/ticket.ts
@@ -10,6 +10,38 @@ export interface PromoCode {
   code: string
   discount_percent: number
   active: boolean
+  /** Redemption cap; `null` / absent = unlimited (events ext >= v1.6.1-aio.12,
+   *  same name as upstream v2). */
+  max_uses?: number | null
+  /** Paid tickets that used this code — derived by the backend on read,
+   *  never sent back. */
+  used_count?: number
+}
+
+/** Body for `POST /events/api/v1/promo/validate/{event_id}` (upstream
+ *  v2 shape; `quantity` stands in for v2's `items` since this fork has
+ *  no ticket types). */
+export interface PromoValidateRequest {
+  codes: string[]
+  quantity: number
+}
+
+export interface BasketDiscount {
+  code: string
+  discount_percent: number | null
+  /** Always null on this fork (percent-only); kept for the v2 shape. */
+  discount_fixed: number | null
+  amount_saved: number
+}
+
+/** Response of the promo validate endpoint. An empty `discounts_applied`
+ *  means none of the submitted codes is valid for this event/quantity. */
+export interface BasketTotals {
+  subtotal: number
+  discount: number
+  total: number
+  discounts_applied: BasketDiscount[]
+  currency: string
 }
 
 /**
@@ -19,7 +51,10 @@ export interface PromoCode {
  * in upstream v1.4.0 (PR #50) and v1.6.0.
  */
 export interface EventExtra {
-  promo_codes: PromoCode[]
+  /** Present on organizer-authenticated records only: public event
+   *  responses (`/events/public`, `/events/{id}`) no longer carry the
+   *  code list (events ext >= v1.6.1-aio.12). */
+  promo_codes?: PromoCode[]
   conditional: boolean
   min_tickets: number
   email_notifications: boolean