stripe: always bill in GBP, never geo-select a currency

/pricing renders "£7" and "£70" as static copy, but checkout sniffed
CF-IPCountry / Accept-Language and passed a matching currency, so Stripe
picked a currency_options rate. A US visitor was shown £7 and charged
$9.99; a German one was charged €7. The page's "Prices in GBP" line was
therefore untrue, and "two months free" only held in GBP and USD (the
EUR annual is €80 against €84, a 4.8% saving).

Displaying one price and billing another is what the UK CPRs and the EU
price-indication rules prohibit, so drop the currency selection rather
than patch the disclosure. Removes _sniff_currency and its country and
locale tables, the currency field on CheckoutRequest, and the now-unused
request parameter.

The currency_options configured on the live Prices are left in place but
unused. Reinstating geo-pricing requires making /pricing currency-aware
first — copy, buttons and the currency-specific saving claim.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

app/routers/stripe_billing.py

@@ -19,7 +19,7 @@ from __future__ import annotations
 
 import asyncio
 import json
-from typing import Any, Literal, Optional
+from typing import Any, Literal
 
 import stripe
 from fastapi import APIRouter, Body, Depends, HTTPException, Request
@@ -75,51 +75,21 @@ def _price_for(cadence: str) -> str:
     raise HTTPException(status_code=400, detail="cadence must be 'monthly' or 'annual'")
 
 
-# Rough country → currency mapping. Covers the markets we have a stated
+# NOTE: we deliberately never pass `currency` to Stripe, so every
-# rate for; everything else falls back to GBP (the home currency) and
+# checkout bills the Price's base currency — GBP. An earlier version
-# Stripe handles the FX at checkout. Configure the per-currency
+# sniffed CF-IPCountry / Accept-Language and selected a matching
-# unit_amount on each Price's `currency_options` in the Stripe Dashboard
+# `currency_options` entry, but /pricing renders £7 and £70 as static
-# — we just signal which option to use here.
+# copy: a US visitor was shown £7 and charged $9.99. Showing one price
-_COUNTRY_CURRENCY: dict[str, str] = {
+# and billing another is exactly what the UK CPRs and the EU
-    "US": "usd", "CA": "usd",
+# price-indication rules prohibit, so the sniffing was removed rather
-    "GB": "gbp", "IM": "gbp", "JE": "gbp", "GG": "gbp",
+# than the disclosure patched. The `currency_options` still configured
-    **dict.fromkeys((
+# on the Prices in the Dashboard are simply unused.
-        "DE", "FR", "IT", "ES", "PT", "NL", "BE", "IE", "AT", "FI",
+#
-        "GR", "LU", "MT", "CY", "EE", "LV", "LT", "SI", "SK", "HR",
+# To reinstate geo-pricing, /pricing must render the matching currency
-    ), "eur"),
+# in its copy, its buttons AND its annual-saving claim first (the claim
-}
+# is currency-specific: "two months free" is true at £70/£84 and
-
+# $94.99/$119.88, but not at €80/€84). See git history for the removed
-# Accept-Language locale → currency, used when CF-IPCountry is absent.
+# _sniff_currency helper and its country/locale tables.
-# Ambiguous locales (e.g. plain "fr" without region) get EUR because
-# that's the majority outcome.
-_LOCALE_CURRENCY: dict[str, str] = {
-    "en-gb": "gbp", "en": "gbp",
-    "en-us": "usd", "en-ca": "usd",
-    "fr": "eur", "de": "eur", "it": "eur", "es": "eur",
-    "pt": "eur", "nl": "eur",
-}
-
-
-def _sniff_currency(request: Request) -> str:
-    """Best-effort currency detection for new-customer checkouts.
-
-    Order: explicit Cloudflare country header, then Accept-Language
-    (exact match then language-only). GBP as the final fallback. Only
-    consulted when the user has no Stripe customer record yet — Stripe
-    locks currency at customer creation, so an existing customer's
-    currency wins regardless of the request locale.
-    """
-    cc = (request.headers.get("cf-ipcountry") or "").upper()
-    if cc in _COUNTRY_CURRENCY:
-        return _COUNTRY_CURRENCY[cc]
-    al = (request.headers.get("accept-language") or "").lower()
-    first = al.split(",", 1)[0].split(";", 1)[0].strip()
-    if first in _LOCALE_CURRENCY:
-        return _LOCALE_CURRENCY[first]
-    short = first.split("-", 1)[0]
-    if short in _LOCALE_CURRENCY:
-        return _LOCALE_CURRENCY[short]
-    return "gbp"
 
 
 def _stripe_client() -> stripe.StripeClient:
@@ -136,10 +106,6 @@ def _stripe_client() -> stripe.StripeClient:
 
 class CheckoutRequest(BaseModel):
     cadence: Literal["monthly", "annual"]
-    # Optional override; when omitted we sniff from request headers.
-    # Honoured only for first-time checkouts (Stripe locks currency
-    # to the customer at creation).
-    currency: Optional[Literal["gbp", "usd", "eur"]] = None
 
 
 class CheckoutResponse(BaseModel):
@@ -149,7 +115,6 @@ class CheckoutResponse(BaseModel):
 @router.post("/api/stripe/checkout", response_model=CheckoutResponse)
 async def create_checkout(
     body: CheckoutRequest,
-    request: Request,
     session: AsyncSession = Depends(get_session),
     cu: CurrentUser = Depends(require_auth),
 ) -> CheckoutResponse:
@@ -178,13 +143,10 @@ async def create_checkout(
         # referral redemption flow ships.
         "allow_promotion_codes": True,
     }
-    # Multi-currency: for first-time buyers (no stripe_customer_id yet)
+    # No `currency` kwarg — every checkout bills the Price's base
-    # we pass the detected/requested currency. Stripe picks the matching
+    # currency (GBP), matching the static £7 / £70 copy on /pricing.
-    # `currency_options` rate configured on the Price in the Dashboard,
+    # See the note above _stripe_client() before reintroducing one.
-    # then locks that currency to the new customer record. Existing
+    #
-    # customers keep their original currency regardless.
-    if not user.stripe_customer_id:
-        create_kwargs["currency"] = body.currency or _sniff_currency(request)
     # Per-cadence cooling-off treatment:
     #
     # - Annual gets a 14-day free trial. No money moves during the

tests/test_stripe_billing.py

@@ -465,50 +465,69 @@ def test_checkout_endpoint_requires_login(tmp_path):
     assert r.status_code == 401, r.text
 
 
-def test_checkout_passes_sniffed_currency_for_new_customer(tmp_path):
+def test_checkout_never_passes_currency(tmp_path):
-    """First-time buyer (no stripe_customer_id yet) gets the currency
+    """Every checkout bills the Price's base currency (GBP), whatever the
-    sniffed from the request. CF-IPCountry=US → 'usd', and Stripe will
+    visitor's geo headers say.
-    look up the USD currency_option on the Price."""
+
+    /pricing renders "£7" and "£70" as static copy, so selecting a
+    `currency_options` rate would show one price and charge another —
+    a US visitor saw £7 and was billed $9.99. Regression guard: if
+    geo-pricing is ever reinstated, the pricing page must become
+    currency-aware in the same change.
+    """
     client, _, session_cookie = _build_app(tmp_path)
 
-    def asserter(params):
+    seen = []
-        assert params["currency"] == "usd"
 
+    def asserter(params):
+        seen.append(params)
+        assert "currency" not in params, (
+            "no currency may be sent — /pricing advertises GBP only"
+        )
+
+    for headers in (
+        {"cf-ipcountry": "US"},
+        {"cf-ipcountry": "DE"},
+        {"accept-language": "en-US,en;q=0.5"},
+        {},
+    ):
         with patch("app.routers.stripe_billing._stripe_client",
                    return_value=_fake_checkout_client(asserter)):
             r = client.post(
                 "/api/stripe/checkout",
                 json={"cadence": "monthly"},
                 cookies={"cassandra_session": session_cookie},
-            headers={"cf-ipcountry": "US"},
+                headers=headers,
             )
         assert r.status_code == 200, r.text
 
+    assert len(seen) == 4
 
-def test_checkout_body_currency_overrides_sniff(tmp_path):
+
-    """Explicit `currency` in the request body beats header sniffing —
+def test_checkout_rejects_currency_in_body(tmp_path):
-    lets a UK-based buyer choose EUR if they want to."""
+    """The `currency` field is gone from CheckoutRequest. A client that
+    still sends one must not silently get GBP under a USD label — the
+    extra key is simply ignored by pydantic, so assert the call is still
+    currency-free rather than trusting the caller."""
     client, _, session_cookie = _build_app(tmp_path)
 
     def asserter(params):
-        assert params["currency"] == "eur"
+        assert "currency" not in params
 
     with patch("app.routers.stripe_billing._stripe_client",
                return_value=_fake_checkout_client(asserter)):
         r = client.post(
             "/api/stripe/checkout",
-            json={"cadence": "monthly", "currency": "eur"},
+            json={"cadence": "monthly", "currency": "usd"},
             cookies={"cassandra_session": session_cookie},
-            headers={"cf-ipcountry": "GB"},
         )
     assert r.status_code == 200, r.text
 
 
-def test_checkout_omits_currency_for_existing_customer(tmp_path):
+def test_checkout_uses_existing_customer_ref(tmp_path):
-    """Existing customer: Stripe locked their currency at first
+    """Existing customer: use the stored `customer` ref rather than
-    checkout, so passing `currency` again would error. Verify we omit
+    `customer_email`, so repeat checkouts don't mint duplicate Stripe
-    it (and also use the existing `customer` ref instead of
+    customers."""
-    customer_email)."""
     import asyncio
 
     from app.models import User
@@ -524,36 +543,16 @@ def test_checkout_omits_currency_for_existing_customer(tmp_path):
     asyncio.run(_link())
 
     def asserter(params):
-        assert "currency" not in params, (
+        assert "currency" not in params
-            "currency must not be passed once a customer exists — "
-            "Stripe rejects mismatches against the locked customer currency"
-        )
         assert params["customer"] == "cus_existing_xxxxxxxxxxxxxx"
+        assert "customer_email" not in params
 
     with patch("app.routers.stripe_billing._stripe_client",
                return_value=_fake_checkout_client(asserter)):
         r = client.post(
             "/api/stripe/checkout",
-            json={"cadence": "monthly", "currency": "usd"},
+            json={"cadence": "monthly"},
             cookies={"cassandra_session": session_cookie},
             headers={"cf-ipcountry": "US"},
         )
     assert r.status_code == 200, r.text
-
-
-def test_sniff_currency_fallback_chain():
-    """Unit-test the header-sniffing helper: CF country wins, then
-    Accept-Language exact, then language-only, then GBP default."""
-    from types import SimpleNamespace
-
-    from app.routers.stripe_billing import _sniff_currency
-
-    def _req(headers):
-        return SimpleNamespace(headers=headers)
-
-    assert _sniff_currency(_req({"cf-ipcountry": "DE"})) == "eur"
-    assert _sniff_currency(_req({"cf-ipcountry": "us"})) == "usd"  # case-insensitive
-    assert _sniff_currency(_req({"accept-language": "fr-FR,fr;q=0.9"})) == "eur"
-    assert _sniff_currency(_req({"accept-language": "en-US,en;q=0.5"})) == "usd"
-    assert _sniff_currency(_req({"accept-language": "ja,ja-JP;q=0.5"})) == "gbp"
-    assert _sniff_currency(_req({})) == "gbp"