diff --git a/README.md b/README.md
index 2decacf..f92db2b 100644
--- a/README.md
+++ b/README.md
@@ -1175,21 +1175,35 @@ unsynced.
   — a contact's `listIds` on Brevo is only populated once double opt-in
   actually confirms, never for a merely-requested one, so its presence is
   a reliable signal. If already subscribed: skips the resend entirely and
-  returns `{ ok: true, alreadySubscribed: true }` instead, which the UI
-  (`useNewsletterSignup.ts`) surfaces as a different message ("Diese
-  E-Mail-Adresse ist schon für unseren Newsletter angemeldet.") instead of
-  the normal "check your inbox" copy. The check fails open (any error →
-  proceed to the normal signup flow) — it's a UX nicety, never a reason to
-  block a real signup.
+  returns `{ ok: true, alreadySubscribed: true }` instead. The check fails
+  open (any error → proceed to the normal signup flow) — it's a UX
+  nicety, never a reason to block a real signup. **Routed through the
+  existing error state, not a success variant** — per explicit feedback,
+  swapping the whole form out for a bare message (the real-success
+  treatment) felt wrong for "you're already signed up, nothing to do"; the
+  form stays visible with a small red note below it instead, exactly like
+  every other inline validation error (`useNewsletterSignup.ts` sets
+  `status: "error"`, `error: "Diese E-Mail-Adresse ist schon für unseren
+  Newsletter angemeldet."` — no new UI needed in any of the 4 forms, they
+  already render `{status === "error" && <p className="text-red-600
+  ...">{error}</p>}`).
 - **`app/lib/useNewsletterSignup.ts`** — the shared email/consent/submit
   state + on-blur validation + refocus-on-invalid-submit behind all four
   forms (same "state of the art, simple" input-quality bar as checkout's
   own fields). Each form keeps its own markup/visual style (`Newsletter`'s
   panel layout, `/challenge`'s hardcoded-hex-color palette, etc.) — only
-  the logic is shared, not a one-size-fits-all component. The success
-  message text itself also now lives here (`successMessage`), not
-  hardcoded 4 times per form — one of two variants depending on
-  `alreadySubscribed`.
+  the logic is shared, not a one-size-fits-all component. The real-success
+  message text also now lives here (`successMessage`) instead of
+  hardcoded 4 times per form.
+- **A misconfigured `BREVO_LIST_ID` in Coolify (`2` instead of `5`) broke
+  every newsletter signup in production for a stretch of time** —
+  discovered and fixed 2026-07-25 while testing the already-subscribed
+  feature above. The generic customer-facing error message ("Anmeldung ist
+  fehlgeschlagen...") gave no hint why; `upsertNewsletterContact()`'s real
+  `reason` was silently discarded by `/api/newsletter/subscribe/route.ts`
+  before this, now `console.error`'d server-side (message still stays
+  generic to the customer — never leak Brevo's internal error text, just
+  no longer *undiagnosable*).
 - **`app/lib/email.ts`** — `isValidEmail()`/`validateEmailFormat()`,
   the single plain-email-format check shared by every newsletter form
   *and* checkout's own email field (previously duplicated between
diff --git a/app/lib/useNewsletterSignup.ts b/app/lib/useNewsletterSignup.ts
index 7a56c18..0560970 100644
--- a/app/lib/useNewsletterSignup.ts
+++ b/app/lib/useNewsletterSignup.ts
@@ -9,11 +9,14 @@ import type { NewsletterOptInSource } from "./brevo";
 // hero form, /challenge's EmailCapture) — four places with the same
 // email+consent+submit shape but different markup/visual style, so only
 // the logic is shared here rather than a one-size-fits-all component.
-// Same two sentences every form already showed hardcoded (per the user's
-// own explicit wording request, see the newsletter-DOI memory) — kept
-// here once instead of duplicated across all 4 forms now that a second
-// variant (already subscribed) needs the same treatment.
+// Per the user's own explicit wording request, see the newsletter-DOI
+// memory — kept here once rather than duplicated across all 4 forms.
 const SUCCESS_MESSAGE = "Fast geschafft! Schau kurz in dein Postfach – da wartet schon eine Mail von uns.";
+// Deliberately routed through the *error* state, not a success variant —
+// per explicit feedback: swapping the whole form out for a bare message
+// (the real-success treatment) felt wrong for "you're already signed up,
+// nothing to do" — the form should stay visible, with a small note below
+// it, exactly like every other inline validation error already does.
 const ALREADY_SUBSCRIBED_MESSAGE = "Diese E-Mail-Adresse ist schon für unseren Newsletter angemeldet.";
 
 export function useNewsletterSignup(source: NewsletterOptInSource) {
@@ -22,7 +25,6 @@ export function useNewsletterSignup(source: NewsletterOptInSource) {
   const [consent, setConsent] = useState(false);
   const [status, setStatus] = useState<"idle" | "submitting" | "success" | "error">("idle");
   const [error, setError] = useState("");
-  const [successMessage, setSuccessMessage] = useState(SUCCESS_MESSAGE);
   const emailRef = useRef<HTMLInputElement>(null);
 
   function handleEmailChange(value: string) {
@@ -56,7 +58,11 @@ export function useNewsletterSignup(source: NewsletterOptInSource) {
         setStatus("error");
         return;
       }
-      setSuccessMessage(data.alreadySubscribed ? ALREADY_SUBSCRIBED_MESSAGE : SUCCESS_MESSAGE);
+      if (data.alreadySubscribed) {
+        setError(ALREADY_SUBSCRIBED_MESSAGE);
+        setStatus("error");
+        return;
+      }
       setStatus("success");
     } catch {
       setError("Anmeldung ist fehlgeschlagen. Bitte versuche es später erneut.");
@@ -64,5 +70,5 @@ export function useNewsletterSignup(source: NewsletterOptInSource) {
     }
   }
 
-  return { email, emailError, consent, setConsent, status, error, successMessage, emailRef, handleEmailChange, handleEmailBlur, handleSubmit };
+  return { email, emailError, consent, setConsent, status, error, successMessage: SUCCESS_MESSAGE, emailRef, handleEmailChange, handleEmailBlur, handleSubmit };
 }