diff --git a/app/api/log/route.ts b/app/api/log/route.ts
index 262918e..813197d 100644
--- a/app/api/log/route.ts
+++ b/app/api/log/route.ts
@@ -1,7 +1,7 @@
 import { NextResponse } from 'next/server';
 
 import { authenticateDevice } from '@/lib/device/session';
-import { clientIp } from '@/lib/device/headers';
+import { clientIp, deviceHeader } from '@/lib/device/headers';
 import { checkTransport } from '@/lib/device/transport';
 import { prisma } from '@/lib/db';
 import { rateLimit } from '@/lib/ratelimit';
@@ -34,8 +34,21 @@ export async function POST(request: Request) {
   }
 
   const device = await authenticateDevice(request);
+
   if (!device) {
-    return NextResponse.json({ error: 'Jeton invalide' }, { status: 401 });
+    // A panel that cannot authenticate is precisely the panel whose own
+    // account of the failure is worth having. Refusing it with a 401 threw
+    // away the one diagnostic that mattered here: the firmware was reporting
+    // a 308 on /api/setup/, and we discarded the message saying so.
+    //
+    // Nothing is stored — the rows are tied to a device that does not exist —
+    // but it reaches the server log, where `docker compose logs app` will show
+    // it. The route is rate-limited above, so this is not an open write.
+    const body = await request.text().catch(() => '');
+    console.warn(
+      `[device] journal d'un appareil non authentifié (ID: ${deviceHeader(request, 'id') ?? 'absent'}) : ${body.slice(0, 1000)}`,
+    );
+    return new NextResponse(null, { status: 204 });
   }
 
   let entries: IncomingLog[] = [];
diff --git a/next.config.ts b/next.config.ts
index 845c54c..913669a 100644
--- a/next.config.ts
+++ b/next.config.ts
@@ -8,6 +8,28 @@ const nextConfig: NextConfig = {
   // Next writes its own AGENTS.md/CLAUDE.md otherwise; this project documents
   // itself in README.md and PLAN.md.
   agentRules: false,
+
+  // The panel's HTTP client does not follow redirects: it reports any non-2xx
+  // as "returned code is not OK" and gives up. The firmware asks for
+  // /api/setup/ with a trailing slash, which Next would answer with a 308 —
+  // so the device never obtained a token, then failed /api/display with an
+  // empty one, and reported that it could not reach the API at all.
+  //
+  // Serving both spellings is the fix. The redirect is disabled and the
+  // slashed paths are rewritten, rather than the device being asked to behave
+  // differently: it cannot.
+  skipTrailingSlashRedirect: true,
+  async rewrites() {
+    return [
+      { source: '/api/setup/', destination: '/api/setup' },
+      { source: '/api/display/', destination: '/api/display' },
+      { source: '/api/log/', destination: '/api/log' },
+      { source: '/api/health/', destination: '/api/health' },
+      // Admin pages keep working when someone types the slash by hand, which
+      // Next would otherwise have redirected for us.
+      { source: '/admin/', destination: '/admin' },
+    ];
+  },
   // These must be required from node_modules at runtime, not bundled.
   // satori loads harfbuzz and yoga as WebAssembly by relative path; bundling
   // rewrites that path and the renderer dies with a missing hb.wasm. resvg is
diff --git a/tests/integration/device-api.test.ts b/tests/integration/device-api.test.ts
index a87b521..b5d2c35 100644
--- a/tests/integration/device-api.test.ts
+++ b/tests/integration/device-api.test.ts
@@ -217,11 +217,19 @@ describe.skipIf(!hasDatabase)('device API', () => {
   });
 
   describe('POST /api/log', () => {
-    it('refuses a request with no token', async () => {
+    it('accepts a log from a device that cannot authenticate, without storing it', async () => {
+      // A panel that cannot authenticate is precisely the panel whose account
+      // of the failure is worth having: this is how a 308 on /api/setup/ was
+      // finally diagnosed, after a 401 had been discarding the evidence.
       const response = await log(
-        deviceRequest('/api/log', {}, { method: 'POST', body: '{"logs":[]}' }),
+        deviceRequest(
+          '/api/log',
+          { ID: MAC },
+          { method: 'POST', body: '{"logs":[{"message":"returned code is not OK. Code - 308"}]}' },
+        ),
       );
-      expect(response.status).toBe(401);
+      expect(response.status).toBe(204);
+      expect(await prisma.deviceLog.count()).toBe(0);
     });
 
     it('stores what the firmware reports', async () => {