diff --git a/backend/src/routes/settings.ts b/backend/src/routes/settings.ts
index 9eccc69..4ef1ce1 100644
--- a/backend/src/routes/settings.ts
+++ b/backend/src/routes/settings.ts
@@ -28,7 +28,7 @@ import {
   validateStorageTemplate,
 } from "../services/printService";
 import { getUserMakerworldCookie, setUserMakerworldCookie } from "../services/makerworldCookieService";
-import { verifyMakerworldCookie } from "../services/makerworldCloudApi";
+import { type MakerworldCookieCheck, verifyMakerworldCookie } from "../services/makerworldCloudApi";
 import { verifyThingiverseAccessToken } from "../services/thingiverseApi";
 import { SLICER_IDS, getUserSlicer, setUserSlicer } from "../services/slicerPreferenceService";
 import { THEME_SELECTIONS, getUserTheme, setUserTheme } from "../services/themePreferenceService";
@@ -282,6 +282,17 @@ router.get(
 // tab) and deliberately swallows failures, so adding a live network test there would only add
 // latency for no benefit. Only ProfilePage's manual Save (settingsApi.updateMakerworld) sends
 // `verify: true`.
+const MAKERWORLD_UNVERIFIABLE_MESSAGES: Record<
+  Extract<MakerworldCookieCheck, { result: "unverifiable" }>["reason"],
+  string
+> = {
+  cloudflare_no_flaresolverr:
+    "Couldn't check this cookie: MakerWorld's Cloudflare protection blocked the request and FlareSolverr isn't configured. Set FLARESOLVERR_URL and try again.",
+  flaresolverr_failed:
+    "Couldn't check this cookie: MakerWorld's Cloudflare protection blocked the request and FlareSolverr didn't get past it. Make sure FlareSolverr is running and reachable at FLARESOLVERR_URL, then try again.",
+  network: "Couldn't check this cookie: MakerWorld didn't respond. Check this server's internet connection and try again.",
+};
+
 const makerworldSettingsSchema = z.object({ cookie: z.string().nullable(), verify: z.boolean().optional() });
 router.patch(
   "/settings/makerworld",
@@ -290,11 +301,16 @@ router.patch(
     const trimmed = (body.cookie ?? "").trim();
     // Only a new, non-empty cookie needs testing -- clearing it (trimmed === "") always
     // succeeds, since there's nothing to verify a logged-out state against.
-    if (body.verify && trimmed && !(await verifyMakerworldCookie(trimmed))) {
-      throw new HttpError(
-        422,
-        "Couldn't verify this MakerWorld cookie -- it may be invalid or expired. Copy a fresh Cookie header from a logged-in makerworld.com tab and try again.",
-      );
+    if (body.verify && trimmed) {
+      const check = await verifyMakerworldCookie(trimmed);
+      if (check.result === "invalid") {
+        throw new HttpError(
+          422,
+          "MakerWorld rejected this cookie -- it may be invalid or expired. Copy a fresh Cookie header from a logged-in makerworld.com tab and try again.",
+        );
+      }
+      // 503, not 422: nothing is known to be wrong with the cookie, the check itself couldn't run.
+      if (check.result === "unverifiable") throw new HttpError(503, MAKERWORLD_UNVERIFIABLE_MESSAGES[check.reason]);
     }
     const configured = await setUserMakerworldCookie(req.userId!, body.cookie);
     res.json({ configured });
diff --git a/backend/src/services/makerworldCloudApi.ts b/backend/src/services/makerworldCloudApi.ts
index 1dc778d..1d530de 100644
--- a/backend/src/services/makerworldCloudApi.ts
+++ b/backend/src/services/makerworldCloudApi.ts
@@ -101,15 +101,23 @@ export function extractMakerworldBearerToken(rawCookieOrToken: string | null | u
   return null;
 }
 
+/** Outcome of verifyMakerworldCookie. "unverifiable" means the check never got an answer about
+ * the cookie itself -- Cloudflare challenged the request and FlareSolverr is unset, unreachable,
+ * or couldn't solve it, or MakerWorld didn't respond -- so the cookie may be perfectly fine. */
+export type MakerworldCookieCheck =
+  | { result: "valid" }
+  | { result: "invalid" }
+  | { result: "unverifiable"; reason: "cloudflare_no_flaresolverr" | "flaresolverr_failed" | "network" };
+
 /** Called before storing a cookie pasted into Profile > MakerWorld (see routes/settings.ts'
  * PATCH /settings/makerworld), so a stale/expired/mistyped paste is rejected up front instead of
  * only surfacing as a failed import later. A malformed paste (extractMakerworldBearerToken
  * finding no usable token at all) is rejected without a network call; otherwise this is the
  * same self-profile request api.bambulab.com/MakerWorld clients use right after login, so a 200
  * here means the account is genuinely logged in, not just that the string looks token-shaped. */
-export async function verifyMakerworldCookie(rawCookieOrToken: string): Promise<boolean> {
+export async function verifyMakerworldCookie(rawCookieOrToken: string): Promise<MakerworldCookieCheck> {
   const bearerToken = extractMakerworldBearerToken(rawCookieOrToken);
-  if (!bearerToken) return false;
+  if (!bearerToken) return { result: "invalid" };
   const controller = new AbortController();
   const timeout = setTimeout(() => controller.abort(), CLOUD_API_TIMEOUT_MS);
   try {
@@ -123,18 +131,21 @@ export async function verifyMakerworldCookie(rawCookieOrToken: string): Promise<
       redirect: "follow",
       signal: controller.signal,
     });
-    if (res.status === 403 && isFlaresolverrEnabled() && looksLikeCloudflareBlock(res.headers)) {
+    if (res.status === 403 && looksLikeCloudflareBlock(res.headers)) {
+      // A Cloudflare challenge is about this server's IP, not the token -- it says nothing
+      // either way about the cookie, so without a way past it the answer is "couldn't check".
+      if (!isFlaresolverrEnabled()) return { result: "unverifiable", reason: "cloudflare_no_flaresolverr" };
       // This endpoint answers 200 with an empty body through FlareSolverr's browser when the
       // session isn't actually logged in, so a bare status check would accept any string here.
       // Assert on the parsed body instead -- only a genuinely authenticated session has a `uid`.
       const solved = await fetchViaFlaresolverr(SELF_PREFERENCE_URL, `token=${bearerToken}`);
-      if (!solved) return false;
+      if (!solved) return { result: "unverifiable", reason: "flaresolverr_failed" };
       const data = extractJsonFromBrowserBody(solved.body);
-      return isRecord(data) && data.uid != null;
+      return isRecord(data) && data.uid != null ? { result: "valid" } : { result: "invalid" };
     }
-    return res.ok;
+    return res.ok ? { result: "valid" } : { result: "invalid" };
   } catch {
-    return false;
+    return { result: "unverifiable", reason: "network" };
   } finally {
     clearTimeout(timeout);
   }