diff --git a/lib/hosters.js b/lib/hosters.js
index 17c7d3e..1069243 100644
--- a/lib/hosters.js
+++ b/lib/hosters.js
@@ -325,11 +325,15 @@ async function apiGet(url, signal) {
     try {
       data = JSON.parse(text);
     } catch {
-      throw new Error(`API-Antwort war kein JSON (HTTP ${res.status}): ${(text || '').slice(0, 200)}`);
+      const err = new Error(`API-Antwort war kein JSON (HTTP ${res.status}): ${(text || '').slice(0, 200)}`);
+      if (res.status >= 500) err.transientNetwork = true;
+      throw err;
     }
 
     if (data.status && [401, 403, 429, 500].includes(data.status)) {
-      throw new Error(data.msg || data.message || JSON.stringify(data));
+      const err = new Error(data.msg || data.message || JSON.stringify(data));
+      if (data.status === 500) err.transientNetwork = true;
+      throw err;
     }
     return data;
   } finally {
@@ -342,6 +346,7 @@ async function apiGet(url, signal) {
 
 async function getUploadServer(hosterName, hosterConfig, apiKey, signal) {
   let lastMessage = '';
+  let lastTransient = false;
 
   for (let attempt = 1; attempt <= SERVER_RETRY_ATTEMPTS; attempt++) {
     for (const endpoint of hosterConfig.serverEndpoints) {
@@ -361,6 +366,7 @@ async function getUploadServer(hosterName, hosterConfig, apiKey, signal) {
       } catch (err) {
         if (err.name === 'AbortError') throw err;
         if (err.message) lastMessage = err.message;
+        if (err.transientNetwork === true) lastTransient = true;
       }
     }
 
@@ -394,6 +400,7 @@ async function getUploadServer(hosterName, hosterConfig, apiKey, signal) {
     // Genuine auth failures (invalid key / unauthorized / forbidden) make
     // shouldRetryServerLookup return false and stay classified as account errors.
     if (shouldRetryServerLookup(lastMessage)) e.hosterTransient = true;
+    if (lastTransient) e.transientNetwork = true;
     throw e;
   }
   throw new Error('Kein Upload-Server erhalten. API-Key pruefen.');
@@ -404,7 +411,7 @@ async function _fetchByseFileList(apiKey, signal) {
   // to match the upload we just did against what the server has. The API
   // shape is typical XFS: { status, msg, result: { files: [...] } } or
   // { status, msg, files: [...] }.
-  const url = `https://api.byse.sx/api/file/list?key=${encodeURIComponent(apiKey)}&per_page=100&sort=date&order=desc`;
+  const url = `https://api.byse.sx/file/list?key=${encodeURIComponent(apiKey)}&per_page=100&sort=date&order=desc`;
   try {
     const { body, statusCode } = await request(url, {
       method: 'GET', signal,
@@ -573,9 +580,11 @@ async function uploadFile(hosterName, filePath, apiKey, onProgress, signal, thro
     payload = rawBody ? JSON.parse(rawBody) : {};
   } catch {
     const snippet = rawBody ? rawBody.slice(0, 240).replace(/\s+/g, ' ').trim() : '';
-    throw new Error(
+    const err = new Error(
       `Upload-Antwort von ${hosterName} war kein JSON (HTTP ${statusCode}${snippet ? `): ${snippet}` : ')'}`
     );
+    if (statusCode >= 500) err.transientNetwork = true;
+    throw err;
   }
   // Normalize valid-but-not-object JSON (JSON.parse('null') → null;
   // JSON.parse('"foo"') → string; JSON.parse('[1]') → array). Without this
@@ -589,15 +598,19 @@ async function uploadFile(hosterName, filePath, apiKey, onProgress, signal, thro
   }
 
   if (statusCode < 200 || statusCode >= 300) {
-    throw new Error(
+    const err = new Error(
       payload.msg
       || payload.message
       || `Upload fehlgeschlagen (HTTP ${statusCode}${headers?.['content-type'] ? `, ${headers['content-type']}` : ''})`
     );
+    if (statusCode >= 500) err.transientNetwork = true;
+    throw err;
   }
 
   if (payload.status && [401, 403, 429, 500].includes(payload.status)) {
-    throw new Error(payload.msg || payload.message || JSON.stringify(payload));
+    const err = new Error(payload.msg || payload.message || JSON.stringify(payload));
+    if (payload.status === 500) err.transientNetwork = true;
+    throw err;
   }
 
   let result = null;
diff --git a/lib/upload-manager.js b/lib/upload-manager.js
index f88c026..af52573 100644
--- a/lib/upload-manager.js
+++ b/lib/upload-manager.js
@@ -131,6 +131,7 @@ class UploadManager extends EventEmitter {
   // which takes priority in _shouldSkipRetryOnAccountError.
   _isFileRejectedError(err) {
     if (!err) return false;
+    if (err.transientNetwork === true) return false;
     if (err.accountError === true) return false; // explicit account-level wins
     if (err.fileRejected === true) return true;
     if (!err.message) return false;
@@ -161,7 +162,9 @@ class UploadManager extends EventEmitter {
   // out for this file without blacklisting the account, so other jobs in the
   // batch still get a fresh chance on it.
   _isTransientNetworkError(err) {
-    if (!err || !err.message) return false;
+    if (!err) return false;
+    if (err.transientNetwork === true) return true;
+    if (!err.message) return false;
     const m = String(err.message);
     const TRANSIENT = [
       /ENOTFOUND/i,
@@ -177,7 +180,11 @@ class UploadManager extends EventEmitter {
       /dns (lookup|error|failed)/i,
       /getaddrinfo/i,
       /fetch failed/i,
-      /\bconnect (ETIMEDOUT|ECONN)/i
+      /\bconnect (ETIMEDOUT|ECONN)/i,
+      /HTTP 5\d\d\b/i,
+      /Bad Gateway/i,
+      /Service Unavailable/i,
+      /Gateway Time-?out/i
     ];
     return TRANSIENT.some(p => p.test(m));
   }
@@ -188,6 +195,7 @@ class UploadManager extends EventEmitter {
   // or out of quota.
   _shouldSkipRetryOnAccountError(err) {
     if (!err) return false;
+    if (err.transientNetwork === true) return false;
     // Explicit account-level flag from hoster parsers — highest priority.
     if (err.accountError === true) return true;
     if (!err.message) return false;
@@ -982,6 +990,7 @@ class UploadManager extends EventEmitter {
             if (signal.aborted || this.stopAfterActive) break;
             if (this._isFileRejectedError(err)) break;
             if (this._isHosterTransientError(err)) break;
+            if (this._isTransientNetworkError(err)) break;
             if (attempt >= maxAttempts) break;
           }
         }
diff --git a/tests/byse-reject-recovery.test.js b/tests/byse-reject-recovery.test.js
index 9698b54..9740478 100644
--- a/tests/byse-reject-recovery.test.js
+++ b/tests/byse-reject-recovery.test.js
@@ -40,7 +40,7 @@ test('byse "Not video file format" (suspect) DOES poll recovery and claims the a
   let listCalls = 0;
   requestRouter = async (url, opts) => {
     const u = String(url);
-    if (/\/api\/file\/list/.test(u)) {
+    if (/\/file\/list/.test(u)) {
       listCalls++;
       const body = listCalls === 1
         ? '{"status":200,"result":{"files":[]}}'
@@ -68,7 +68,7 @@ test('byse "Not video file format" with empty poll throws err.suspectReject so r
   let listCalls = 0;
   requestRouter = async (url, opts) => {
     const u = String(url);
-    if (/\/api\/file\/list/.test(u)) {
+    if (/\/file\/list/.test(u)) {
       listCalls++;
       if (listCalls >= 2) abort.abort();
       return { statusCode: 200, headers: {}, body: { text: async () => '{"status":200,"result":{"files":[]}}' } };
@@ -95,7 +95,7 @@ test('byse "Not video file format" with probe-confirmed NON-video skips the reco
   let listCalls = 0;
   requestRouter = async (url, opts) => {
     const u = String(url);
-    if (/\/api\/file\/list/.test(u)) {
+    if (/\/file\/list/.test(u)) {
       listCalls++;
       return { statusCode: 200, headers: {}, body: { text: async () => '{"status":200,"result":{"files":[]}}' } };
     }
@@ -122,7 +122,7 @@ test('byse explicit "Duplicate" rejection still throws fast WITHOUT recovery pol
   let listCalls = 0;
   requestRouter = async (url, opts) => {
     const u = String(url);
-    if (/\/api\/file\/list/.test(u)) {
+    if (/\/file\/list/.test(u)) {
       listCalls++;
       return { statusCode: 200, headers: {}, body: { text: async () => '{"status":200,"result":{"files":[]}}' } };
     }
@@ -149,7 +149,7 @@ test('byse empty filecode WITHOUT explicit rejection still polls recovery', asyn
   let listCalls = 0;
   requestRouter = async (url, opts) => {
     const u = String(url);
-    if (/\/api\/file\/list/.test(u)) {
+    if (/\/file\/list/.test(u)) {
       listCalls++;
       const body = listCalls === 1
         ? '{"status":200,"result":{"files":[]}}'
@@ -170,3 +170,65 @@ test('byse empty filecode WITHOUT explicit rejection still polls recovery', asyn
   assert.strictEqual(res.file_code, 'RECOVERED99');
   assert.ok(listCalls >= 2, 'recovery polling must run when there is no explicit rejection');
 });
+
+function stubBysePost(response) {
+  requestRouter = async (url, opts) => {
+    const u = String(url);
+    if (/\/file\/list/.test(u)) {
+      return { statusCode: 200, headers: {}, body: { text: async () => '{"status":200,"result":{"files":[]}}' } };
+    }
+    if (opts && opts.body && typeof opts.body[Symbol.asyncIterator] === 'function') {
+      for await (const chunk of opts.body) { if (chunk && chunk.length === -1) break; }
+    }
+    return response();
+  };
+}
+
+test('byse upload POST 502 (HTML gateway body) is tagged transientNetwork', async () => {
+  stubByseUploadServer();
+  stubBysePost(() => ({
+    statusCode: 502,
+    headers: { 'content-type': 'text/html' },
+    body: { text: async () => '<!doctype html><html><head><title>502 Bad Gateway</title></head><body>502 Bad Gateway</body></html>' }
+  }));
+  await assert.rejects(
+    () => uploadFile('byse.sx', tmpFile, 'VALIDKEY', null, null, null),
+    (err) => err.transientNetwork === true && /kein JSON \(HTTP 502\)/.test(err.message)
+  );
+});
+
+test('byse upload POST non-2xx JSON 503 is tagged transientNetwork', async () => {
+  stubByseUploadServer();
+  stubBysePost(() => ({
+    statusCode: 503,
+    headers: { 'content-type': 'application/json' },
+    body: { text: async () => JSON.stringify({ status: 503, msg: 'Service Unavailable' }) }
+  }));
+  await assert.rejects(
+    () => uploadFile('byse.sx', tmpFile, 'VALIDKEY', null, null, null),
+    (err) => err.transientNetwork === true
+  );
+});
+
+test('byse upload POST 2xx envelope {status:500} is transient; {status:403} stays account-level', async () => {
+  stubByseUploadServer();
+  stubBysePost(() => ({
+    statusCode: 200,
+    headers: { 'content-type': 'application/json' },
+    body: { text: async () => JSON.stringify({ status: 500, msg: 'Internal Server Error' }) }
+  }));
+  await assert.rejects(
+    () => uploadFile('byse.sx', tmpFile, 'VALIDKEY', null, null, null),
+    (err) => err.transientNetwork === true
+  );
+
+  stubBysePost(() => ({
+    statusCode: 200,
+    headers: { 'content-type': 'application/json' },
+    body: { text: async () => JSON.stringify({ status: 403, msg: 'Forbidden' }) }
+  }));
+  await assert.rejects(
+    () => uploadFile('byse.sx', tmpFile, 'VALIDKEY', null, null, null),
+    (err) => err.transientNetwork !== true
+  );
+});
diff --git a/tests/suspect-reject-alternates.test.js b/tests/suspect-reject-alternates.test.js
index dc95654..81e860a 100644
--- a/tests/suspect-reject-alternates.test.js
+++ b/tests/suspect-reject-alternates.test.js
@@ -250,4 +250,31 @@ describe('suspect-reject alternate accounts', () => {
     assert.equal(summary.failed, 1);
     assert.equal(mockUploadFile.mock.calls.length, 1);
   });
+
+  it('a transient 5xx (byse 502) retries the SAME account and fails clean — no blacklist, no failover cascade', async () => {
+    const mgr = poolMgr([
+      { id: 'acc1', apiKey: 'key1' },
+      { id: 'acc2', apiKey: 'key2' },
+      { id: 'acc3', apiKey: 'key3' }
+    ], { retries: 2 });
+    mgr._sleep = async () => {};
+    mockUploadFile.mock.mockImplementation(async () => {
+      const e = new Error('Upload-Antwort von byse.sx war kein JSON (HTTP 502): <!doctype html>');
+      e.transientNetwork = true;
+      throw e;
+    });
+    let accountFailed = 0;
+    mgr.on('account-failed', () => { accountFailed++; });
+    let summary = null;
+    mgr.on('batch-done', (s) => { summary = s; });
+
+    await mgr.startBatch([{ file: '/test/big.mkv', hoster: 'byse.sx', apiKey: 'key1', accountId: 'acc1' }]);
+
+    assert.equal(summary.failed, 1);
+    assert.equal(accountFailed, 0, 'a transient 502 must never emit account-failed');
+    assert.equal(mgr.getFailedAccountKeys().length, 0, 'no account blacklisted on a transient 502');
+    const keys = mockUploadFile.mock.calls.map(c => c.arguments[2]);
+    assert.ok(keys.length >= 2, 'the 502 is retried on the same account');
+    assert.ok(keys.every(k => k === 'key1'), 'every attempt stays on the primary — no cascade to key2/key3');
+  });
 });
diff --git a/tests/upload-manager.test.js b/tests/upload-manager.test.js
index 7c10273..ed454c6 100644
--- a/tests/upload-manager.test.js
+++ b/tests/upload-manager.test.js
@@ -847,6 +847,45 @@ describe('UploadManager', () => {
       assert.equal(mgr._shouldSkipRetryOnAccountError(err), false);
     });
 
+    it('transientNetwork flag is recognised even with an empty/absent message', () => {
+      const mgr = new UploadManager({});
+      const flagged = new Error('');
+      flagged.transientNetwork = true;
+      assert.equal(mgr._isTransientNetworkError(flagged), true, 'flag must win before the empty-message guard');
+      assert.equal(mgr._isFileRejectedError(flagged), false);
+      assert.equal(mgr._isHosterTransientError(flagged), false);
+      assert.equal(mgr._shouldSkipRetryOnAccountError(flagged), false);
+
+      const flaggedHtml = new Error('Upload-Antwort von byse.sx war kein JSON (HTTP 502): <!doctype html> forbidden duplicate');
+      flaggedHtml.transientNetwork = true;
+      assert.equal(mgr._isTransientNetworkError(flaggedHtml), true);
+      assert.equal(mgr._shouldSkipRetryOnAccountError(flaggedHtml), false, 'flag overrides any account-keyword in the 502 HTML snippet');
+      assert.equal(mgr._isFileRejectedError(flaggedHtml), false, 'flag overrides any rejection-keyword in the 502 HTML snippet');
+    });
+
+    it('5xx / gateway errors classify transient by message (defensive fallback), 4xx stay account-level', () => {
+      const mgr = new UploadManager({});
+      const transient = [
+        'Upload-Antwort von byse.sx war kein JSON (HTTP 502): <!doctype html>',
+        'Upload fehlgeschlagen (HTTP 503, text/html)',
+        'HTTP 504 Gateway Time-out',
+        'Bad Gateway',
+        'Service Unavailable'
+      ];
+      for (const msg of transient) {
+        assert.equal(mgr._isTransientNetworkError(new Error(msg)), true, `should be transient: ${msg}`);
+      }
+      const accountLevel = [
+        'Upload fehlgeschlagen (HTTP 429, application/json)',
+        'HTTP 403 Forbidden',
+        'HTTP 401 Unauthorized'
+      ];
+      for (const msg of accountLevel) {
+        assert.equal(mgr._isTransientNetworkError(new Error(msg)), false, `must NOT be transient: ${msg}`);
+        assert.equal(mgr._shouldSkipRetryOnAccountError(new Error(msg)), true, `must stay account-level: ${msg}`);
+      }
+    });
+
     it('hoster-transient regex fallback catches wrapped doodstream empty-form errors', () => {
       const mgr = new UploadManager({});
       const cases = [