diff --git a/frontend/src/__tests__/pages/ingest-csv.test.tsx b/frontend/src/__tests__/pages/ingest-csv.test.tsx
index a5056e59b..d13d2749a 100644
--- a/frontend/src/__tests__/pages/ingest-csv.test.tsx
+++ b/frontend/src/__tests__/pages/ingest-csv.test.tsx
@@ -160,6 +160,21 @@ describe('CSV import results on /ingest', () => {
     expect(mocks.ingestFile).not.toHaveBeenCalled();
   });
 
+  it('shows the API-key save error on the URL tab without sending a request', async () => {
+    mocks.storeApiKey.mockRejectedValue(new Error('API key could not be saved. Please try again.'));
+    render(<IngestPage />);
+    await userEvent.click(screen.getByRole('tab', { name: /url ingestion/i }));
+    fireEvent.change(screen.getByPlaceholderText('rge_...'), { target: { value: 'rge_replacement_key' } }); // pragma: allowlist secret
+    fireEvent.change(screen.getByPlaceholderText('https://example.com/regulatory-document.pdf'), {
+      target: { value: 'https://example.com/regulatory-document.pdf' },
+    });
+    await userEvent.click(screen.getByRole('button', { name: /ingest|upload & process/i }));
+
+    expect(await screen.findByText('API key could not be saved. Please try again.')).toBeInTheDocument();
+    expect(screen.getByText('Ingestion Failed')).toBeInTheDocument();
+    expect(mocks.ingestURL).not.toHaveBeenCalled();
+  });
+
   it('offers the CTE Jev suggested and re-uploads with it only on confirmation', async () => {
     const rejected = Object.assign(new Error('No valid rows found: Row 2: No CTE type'), {
       response: {
diff --git a/frontend/src/__tests__/pages/ingest-epcis-batch-errors.test.tsx b/frontend/src/__tests__/pages/ingest-epcis-batch-errors.test.tsx
new file mode 100644
index 000000000..eb89af9df
--- /dev/null
+++ b/frontend/src/__tests__/pages/ingest-epcis-batch-errors.test.tsx
@@ -0,0 +1,159 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+import { fireEvent, render, screen } from '@testing-library/react';
+import userEvent from '@testing-library/user-event';
+import IngestPage from '@/app/ingest/page';
+
+const mocks = vi.hoisted(() => ({
+  ingestURL: vi.fn(),
+  ingestFile: vi.fn(),
+  ingestEpcisEvent: vi.fn(),
+  ingestEpcisBatch: vi.fn(),
+  ingestEpcisXml: vi.fn(),
+  validateEpcis: vi.fn(),
+  getIngestionJob: vi.fn(),
+  refresh: vi.fn(),
+  storeApiKey: vi.fn(),
+}));
+
+vi.mock('@/lib/auth-context', () => ({
+  useAuth: () => ({ apiKey: 'cookie-managed', setApiKey: mocks.storeApiKey }), // pragma: allowlist secret
+}));
+vi.mock('@/hooks/use-api', () => ({
+  useIngestURL: () => ({ mutateAsync: mocks.ingestURL, reset: vi.fn(), isPending: false, isError: false }),
+  useIngestFile: () => ({ mutateAsync: mocks.ingestFile, reset: vi.fn(), isPending: false, isError: false }),
+  useIngestEpcisEvent: () => ({ mutateAsync: mocks.ingestEpcisEvent, reset: vi.fn(), isPending: false }),
+  useIngestEpcisBatch: () => ({ mutateAsync: mocks.ingestEpcisBatch, reset: vi.fn(), isPending: false }),
+  useIngestEpcisXml: () => ({ mutateAsync: mocks.ingestEpcisXml, reset: vi.fn(), isPending: false }),
+  useValidateEpcisEvent: () => ({ mutateAsync: mocks.validateEpcis, reset: vi.fn(), isPending: false }),
+}));
+vi.mock('@/lib/api-client', () => ({
+  apiClient: { getIngestionJob: mocks.getIngestionJob },
+}));
+vi.mock('@/hooks/use-dashboard-refresh', () => ({
+  notifyDashboardRefresh: mocks.refresh,
+}));
+vi.mock('@/app/ingest/NormalizedDocumentViewer', () => ({
+  NormalizedDocumentViewer: () => <div>Normalized document viewer</div>,
+}));
+
+// Data-free placeholders: two {} events. Shapes below are copied from the
+// backend source; counts derive from EVENTS.length.
+const EVENTS: Record<string, unknown>[] = [{}, {}];
+
+// _validate_epcis (services/ingestion/app/epcis/validation.py) output for {},
+// in order.
+const BACKEND_EVENT_ERRORS = [
+  ...['type', 'eventTime', 'action', 'bizStep'].map((field) => `Missing required EPCIS field '${field}'`),
+  'Unsupported EPCIS event type',
+  'Missing traceability lot code (fsma:traceabilityLotCode or cbvmda:lotNumber)',
+];
+const STATUS = 400;
+const JOINED = BACKEND_EVENT_ERRORS.join(': ');
+// Exact message from _ingest_batch_events_db_atomic (persistence.py).
+const ATOMIC_MESSAGE =
+  'One or more events failed pre-DB validation. No events were persisted. '
+  + 'Use ?mode=partial to opt in to per-event processing with HTTP 207 semantics.';
+
+function axiosRejection(status: number, data: unknown) {
+  return Object.assign(new Error(`Request failed with status code ${status}`), { response: { status, data } });
+}
+
+// Atomic (default, _batch_transactional()): HTTPException(400, detail={...}).
+function atomicRejection(events: unknown[]) {
+  return axiosRejection(STATUS, {
+    detail: {
+      error: 'batch_validation_failed',
+      mode: 'atomic',
+      message: ATOMIC_MESSAGE,
+      errors: events.map((_, index) => ({ index, status_code: STATUS, detail: { errors: BACKEND_EVENT_ERRORS } })),
+    },
+  });
+}
+
+// Partial (?mode=partial or EPCIS_BATCH_TRANSACTIONAL=false): router.py
+// returns the payload itself with status 400, no detail wrapper.
+function partialRejection(events: unknown[]) {
+  return axiosRejection(STATUS, {
+    total: events.length,
+    created: 0,
+    failed: events.length,
+    results: [],
+    errors: events.map((_, index) => ({ index, detail: { errors: BACKEND_EVENT_ERRORS } })),
+    mode: 'partial',
+  });
+}
+
+async function uploadBatch() {
+  render(<IngestPage />);
+  await userEvent.click(screen.getByRole('tab', { name: /epcis 2\.0/i }));
+  const input = document.getElementById('epcis-file-upload') as HTMLInputElement;
+  fireEvent.change(input, {
+    target: { files: [new File([JSON.stringify(EVENTS)], 'events.json', { type: 'application/json' })] },
+  });
+  await userEvent.click(screen.getByRole('button', { name: /upload & process/i }));
+}
+
+function expectEveryEventListed() {
+  for (let index = 0; index < EVENTS.length; index += 1) {
+    expect(screen.getByText(`Event ${index + 1}: ${JOINED}`)).toBeInTheDocument();
+  }
+  expect(screen.getAllByText(/^Event \d+:/)).toHaveLength(EVENTS.length);
+}
+
+describe('EPCIS all-failed batch shows per-event errors', () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it('lists every event under the atomic message', async () => {
+    mocks.ingestEpcisBatch.mockRejectedValue(atomicRejection(EVENTS));
+    await uploadBatch();
+    expect(await screen.findByText('Ingestion Failed')).toBeInTheDocument();
+    expect(screen.getByText(ATOMIC_MESSAGE)).toBeInTheDocument();
+    expectEveryEventListed();
+    expect(mocks.refresh).not.toHaveBeenCalled();
+  });
+
+  it('lists every event for a partial-mode 400 body', async () => {
+    const rejection = partialRejection(EVENTS);
+    mocks.ingestEpcisBatch.mockRejectedValue(rejection);
+    await uploadBatch();
+    expect(await screen.findByText('Ingestion Failed')).toBeInTheDocument();
+    expect(screen.getByText(rejection.message)).toBeInTheDocument();
+    expectEveryEventListed();
+    expect(mocks.refresh).not.toHaveBeenCalled();
+  });
+
+  it('shows the single-event 400 once, with no Event N: lines', async () => {
+    // Single-event path: persistence.py raises
+    // HTTPException(400, detail={"errors": [...]}) for {}.
+    mocks.ingestEpcisEvent.mockRejectedValue(axiosRejection(STATUS, { detail: { errors: BACKEND_EVENT_ERRORS } }));
+    render(<IngestPage />);
+    await userEvent.click(screen.getByRole('tab', { name: /epcis 2\.0/i }));
+    const input = document.getElementById('epcis-file-upload') as HTMLInputElement;
+    fireEvent.change(input, {
+      target: { files: [new File([JSON.stringify(EVENTS[0])], 'event.json', { type: 'application/json' })] },
+    });
+    await userEvent.click(screen.getByRole('button', { name: /upload & process/i }));
+    expect(await screen.findByText('Ingestion Failed')).toBeInTheDocument();
+    expect(screen.getAllByText(JOINED)).toHaveLength(1);
+    expect(screen.queryAllByText(/^Event \d+:/)).toHaveLength(0);
+    expect(mocks.ingestEpcisBatch).not.toHaveBeenCalled();
+  });
+
+  it('clears the previous per-event errors when the API-key save fails', async () => {
+    mocks.ingestEpcisBatch.mockRejectedValue(atomicRejection(EVENTS));
+    await uploadBatch();
+    expect(await screen.findByText('Ingestion Failed')).toBeInTheDocument();
+    expectEveryEventListed();
+
+    mocks.storeApiKey.mockRejectedValue(new Error('API key could not be saved. Please try again.'));
+    fireEvent.change(screen.getByPlaceholderText('rge_...'), { target: { value: 'rge_replacement_key' } }); // pragma: allowlist secret
+    await userEvent.click(screen.getByRole('button', { name: /upload & process/i }));
+
+    expect(await screen.findByText('API key could not be saved. Please try again.')).toBeInTheDocument();
+    expect(screen.queryAllByText(/^Event \d+:/)).toHaveLength(0);
+    expect(screen.queryByText(ATOMIC_MESSAGE)).not.toBeInTheDocument();
+    expect(mocks.ingestEpcisBatch).toHaveBeenCalledTimes(1);
+  });
+});
diff --git a/frontend/src/__tests__/pages/ingest-epcis.test.tsx b/frontend/src/__tests__/pages/ingest-epcis.test.tsx
index ccdacf7aa..d5f5dfb65 100644
--- a/frontend/src/__tests__/pages/ingest-epcis.test.tsx
+++ b/frontend/src/__tests__/pages/ingest-epcis.test.tsx
@@ -162,11 +162,11 @@ describe('EPCIS 2.0 import on /ingest', () => {
     expect(mocks.ingestEpcisEvent).not.toHaveBeenCalled();
     expect(mocks.ingestEpcisXml).not.toHaveBeenCalled();
     expect(mocks.validateEpcis).not.toHaveBeenCalled();
-    // Atomic (default) rejection: the page shows detail.message only. The
-    // per-event errors carry no msg/message key, so detailToMessage drops them.
+    // Atomic (default) rejection: detail.message heads one line per event.
     expect(await screen.findByText('Ingestion Failed')).toBeInTheDocument();
     expect(screen.getByText(ATOMIC_BATCH_MESSAGE)).toBeInTheDocument();
-    expect(screen.queryByText(/^Event \d+:/)).not.toBeInTheDocument();
+    expectEveryEventRejected(eventList.length);
+    expect(screen.getAllByText(/^Event \d+:/)).toHaveLength(eventList.length);
     expect(mocks.refresh).not.toHaveBeenCalled();
   });
 
@@ -184,11 +184,12 @@ describe('EPCIS 2.0 import on /ingest', () => {
       apiKey: 'cookie-managed', // pragma: allowlist secret
       events,
     });
-    // Partial rejection: the body has no detail key, so the page falls back
-    // to the error message and shows no per-event errors.
+    // Partial rejection: the body has no detail key, so the error message is
+    // the heading and the body's errors give one line per event.
     expect(await screen.findByText('Ingestion Failed')).toBeInTheDocument();
     expect(screen.getByText(rejection.message)).toBeInTheDocument();
-    expect(screen.queryByText(/^Event \d+:/)).not.toBeInTheDocument();
+    expectEveryEventRejected(events.length);
+    expect(screen.getAllByText(/^Event \d+:/)).toHaveLength(events.length);
     expect(mocks.refresh).not.toHaveBeenCalled();
   });
 
diff --git a/frontend/src/app/ingest/page.tsx b/frontend/src/app/ingest/page.tsx
index b30ade7ea..ab8670b68 100644
--- a/frontend/src/app/ingest/page.tsx
+++ b/frontend/src/app/ingest/page.tsx
@@ -32,6 +32,7 @@ import {
   parseEpcisJson,
   normalizeEpcisIngestResult,
   epcisErrorMessage,
+  epcisErrorEventMessages,
   type ParsedEpcisJson,
 } from '@/lib/epcis-upload';
 import { notifyDashboardRefresh } from '@/hooks/use-dashboard-refresh';
@@ -122,6 +123,9 @@ export default function IngestPage() {
   const [jobId, setJobId] = useState<string | null>(null);
   const [jobStatus, setJobStatus] = useState<string>('queued');
   const [statusError, setStatusError] = useState<string | null>(null);
+  // URL-tab error for a failed API-key save; URL ingest errors otherwise come
+  // from ingestMutation, which has no setter.
+  const [urlError, setUrlError] = useState<string | null>(null);
   // Dashboard "No data yet" tiles deep-link to /ingest?tab=file (CSV upload).
   const [activeTab, setActiveTab] = useState<string>(() => {
     const tab = searchParams.get('tab');
@@ -133,6 +137,7 @@ export default function IngestPage() {
   const [epcisFile, setEpcisFile] = useState<File | null>(null);
   const [epcisResult, setEpcisResult] = useState<NormalizedEpcisResult | null>(null);
   const [epcisError, setEpcisError] = useState<string | null>(null);
+  const [epcisErrorEvents, setEpcisErrorEvents] = useState<string[]>([]);
   const [epcisValidation, setEpcisValidation] = useState<{
     checked: number;
     valid: number;
@@ -171,6 +176,7 @@ export default function IngestPage() {
       setEpcisFile(e.target.files[0]);
       setEpcisResult(null);
       setEpcisError(null);
+      setEpcisErrorEvents([]);
       setEpcisValidation(null);
     }
   };
@@ -210,6 +216,26 @@ export default function IngestPage() {
   // browser proxy reads it from the cookie, then clear prior result state.
   // Returns false when the caller should stop without sending any request.
   const prepareSubmit = async (): Promise<boolean> => {
+    // Clear the previous upload's results and errors first, so a failed
+    // API-key save below never leaves stale error lines on screen.
+    setJobId(null);
+    setJobStatus('queued');
+    setStatusError(null);
+    setCsvResult(null);
+    setCsvError(null);
+    setCteSuggestion(null);
+    setErrorColumnSuggestions([]);
+    setEpcisResult(null);
+    setEpcisError(null);
+    setEpcisErrorEvents([]);
+    setEpcisValidation(null);
+    setUrlError(null);
+    ingestMutation.reset();
+    ingestFileMutation.reset();
+    ingestEpcisEventMutation.reset();
+    ingestEpcisBatchMutation.reset();
+    ingestEpcisXmlMutation.reset();
+    validateEpcisMutation.reset();
     // Store the API key for future use
     if (!isAuthenticated && apiKey !== storedApiKey) {
       // The browser proxy reads the cookie written by setApiKey and ignores
@@ -221,20 +247,10 @@ export default function IngestPage() {
         const message = error instanceof Error ? error.message : 'Unable to save API key';
         if (activeTab === 'file') setCsvError(message);
         else if (activeTab === 'epcis') setEpcisError(message);
-        else setStatusError(message);
+        else setUrlError(message);
         return false;
       }
     }
-    setJobId(null);
-    setJobStatus('queued');
-    setStatusError(null);
-    setCsvResult(null);
-    setCsvError(null);
-    setCteSuggestion(null);
-    setErrorColumnSuggestions([]);
-    setEpcisResult(null);
-    setEpcisError(null);
-    setEpcisValidation(null);
     return true;
   };
 
@@ -308,6 +324,7 @@ export default function IngestPage() {
       notifyDashboardRefresh();
     } catch (error) {
       setEpcisError(epcisErrorMessage(error));
+      setEpcisErrorEvents(epcisErrorEventMessages(error));
     } finally {
       submitInFlightRef.current = false;
       setIsSubmitting(false);
@@ -818,14 +835,17 @@ export default function IngestPage() {
                     </Callout>
                   )}
 
-                  {((activeTab === 'url' && ingestMutation.isError) || (activeTab === 'file' && csvError) || (activeTab === 'epcis' && epcisError)) && (
+                  {((activeTab === 'url' && (urlError || ingestMutation.isError)) || (activeTab === 'file' && csvError) || (activeTab === 'epcis' && epcisError)) && (
                     <Callout tone="danger" role="alert" className="mt-4">
                       <h4 className="font-medium text-re-text-primary">
                         Ingestion Failed
                       </h4>
                       <p className="mt-1">
-                        {(activeTab === 'file' ? csvError : activeTab === 'epcis' ? epcisError : ingestMutation.error?.message) || 'An error occurred during ingestion'}
+                        {(activeTab === 'file' ? csvError : activeTab === 'epcis' ? epcisError : urlError || ingestMutation.error?.message) || 'An error occurred during ingestion'}
                       </p>
+                      {activeTab === 'epcis' && epcisErrorEvents.map((message, index) => (
+                        <p key={index} className="mt-2">{message}</p>
+                      ))}
                       {activeTab === 'file' && (
                         <ColumnSuggestionList suggestions={errorColumnSuggestions} />
                       )}
@@ -878,7 +898,9 @@ export default function IngestPage() {
                         setEpcisFile(null);
                         setEpcisResult(null);
                         setEpcisError(null);
+                        setEpcisErrorEvents([]);
                         setEpcisValidation(null);
+                        setUrlError(null);
                         setJobId(null);
                         setJobStatus('queued');
                         ingestMutation.reset();
diff --git a/frontend/src/lib/epcis-upload.ts b/frontend/src/lib/epcis-upload.ts
index fda18c2d6..2de962658 100644
--- a/frontend/src/lib/epcis-upload.ts
+++ b/frontend/src/lib/epcis-upload.ts
@@ -111,6 +111,27 @@ export function normalizeEpcisIngestResult(data: EpcisIngestResponse | null | un
   return { total, accepted, rejected, errorMessages };
 }
 
+/**
+ * Per-event lines for a rejected batch, in both backend shapes:
+ * atomic (400, detail {error, mode, message, errors:[{index, status_code, detail}]})
+ * and partial (400 body with no detail wrapper: {errors:[{index, detail}], ...}).
+ * Returns [] for any other failure.
+ */
+export function epcisErrorEventMessages(error: unknown): string[] {
+  if (!(error instanceof Error)) return [];
+  const data = (error as Error & { response?: { data?: unknown } }).response?.data;
+  if (!isRecord(data)) return [];
+  const source = isRecord(data.detail) ? data.detail : data;
+  if (!Array.isArray(source.errors)) return [];
+  const messages: string[] = [];
+  for (const entry of source.errors) {
+    if (!isRecord(entry) || typeof entry.index !== 'number') continue;
+    const message = resultItemMessage(entry as { index?: number; detail?: unknown });
+    if (message && !messages.includes(message)) messages.push(message);
+  }
+  return messages;
+}
+
 /** Render a backend or network failure the same terse way the CSV tab does. */
 export function epcisErrorMessage(error: unknown): string {
   if (error instanceof Error) {