diff --git a/client/src/pages/Settings.tsx b/client/src/pages/Settings.tsx
index b1a4436..dd7d7c8 100644
--- a/client/src/pages/Settings.tsx
+++ b/client/src/pages/Settings.tsx
@@ -16,6 +16,7 @@ interface EtsyStatus {
 interface EtsyConfig {
   configured: boolean;
   apiKeyMasked: string | null;
+  sharedSecretMasked: string | null;
   redirectUri: string | null;
   source: 'database' | 'environment' | null;
 }
@@ -33,6 +34,7 @@ const Settings = () => {
   const [etsyStatus, setEtsyStatus] = useState<EtsyStatus | null>(null);
   const [etsyConfig, setEtsyConfig] = useState<EtsyConfig | null>(null);
   const [apiKeyInput, setApiKeyInput] = useState('');
+  const [sharedSecretInput, setSharedSecretInput] = useState('');
   const [redirectUriInput, setRedirectUriInput] = useState('');
   const [isSavingConfig, setIsSavingConfig] = useState(false);
   const [isConnecting, setIsConnecting] = useState(false);
@@ -90,10 +92,12 @@ const Settings = () => {
     try {
       await api.put('/etsy/config', {
         apiKey: apiKeyInput.trim() || undefined,
+        sharedSecret: sharedSecretInput.trim() || undefined,
         redirectUri: redirectUriInput.trim(),
       });
       toast.success('Etsy configuration saved');
       setApiKeyInput('');
+      setSharedSecretInput('');
       loadEtsyConfig();
     } catch (error: any) {
       toast.error(error.response?.data?.message || 'Failed to save Etsy configuration');
@@ -266,6 +270,24 @@ const Settings = () => {
                   onChange={(e) => setApiKeyInput(e.target.value)}
                 />
               </div>
+              <div>
+                <label className="block text-sm font-medium text-gray-700 mb-1">
+                  Shared Secret
+                </label>
+                <input
+                  type="password"
+                  autoComplete="off"
+                  placeholder={etsyConfig?.sharedSecretMasked
+                    ? `Saved (${etsyConfig.sharedSecretMasked}) — enter a new value to replace it`
+                    : 'Paste the shared secret shown next to your keystring'}
+                  className="w-full px-3 py-2 border border-gray-300 rounded-md focus:ring-2 focus:ring-orange-500 focus:border-transparent"
+                  value={sharedSecretInput}
+                  onChange={(e) => setSharedSecretInput(e.target.value)}
+                />
+                <p className="text-xs text-gray-500 mt-1">
+                  Etsy requires this for API calls — it's on the same page as your keystring.
+                </p>
+              </div>
               <div>
                 <label className="block text-sm font-medium text-gray-700 mb-1">
                   Callback URL
diff --git a/server/.env.example b/server/.env.example
index 395f5b8..8d1ba37 100644
--- a/server/.env.example
+++ b/server/.env.example
@@ -15,4 +15,5 @@ SESSION_SECRET=your-super-secret-session-key-change-this-in-production
 # Etsy API (optional fallback — normally configured per user in the
 # Settings UI and stored in the database)
 # ETSY_API_KEY=your-etsy-keystring
+# ETSY_SHARED_SECRET=your-etsy-shared-secret
 # ETSY_REDIRECT_URI=https://etsy.plexultra.com/api/etsy/callback
\ No newline at end of file
diff --git a/server/src/models/EtsySettings.ts b/server/src/models/EtsySettings.ts
index 755213a..03b6ac4 100644
--- a/server/src/models/EtsySettings.ts
+++ b/server/src/models/EtsySettings.ts
@@ -5,6 +5,9 @@ import mongoose, { Document, Schema } from 'mongoose';
 export interface IEtsySettings extends Document {
   userId: mongoose.Types.ObjectId;
   apiKey: string;
+  // Etsy requires the app's shared secret in the x-api-key header for API
+  // calls; the keystring (apiKey) is the OAuth client id
+  sharedSecret?: string;
   redirectUri: string;
   dateUpdated: Date;
 }
@@ -12,6 +15,7 @@ export interface IEtsySettings extends Document {
 const EtsySettingsSchema: Schema = new Schema({
   userId: { type: Schema.Types.ObjectId, ref: 'User', required: true, unique: true, index: true },
   apiKey: { type: String, required: true, trim: true },
+  sharedSecret: { type: String, trim: true },
   redirectUri: { type: String, required: true, trim: true },
   dateUpdated: { type: Date, default: Date.now },
 });
diff --git a/server/src/routes/etsy.ts b/server/src/routes/etsy.ts
index 86de0b7..077b554 100644
--- a/server/src/routes/etsy.ts
+++ b/server/src/routes/etsy.ts
@@ -30,6 +30,7 @@ const prunePending = () => {
 
 interface EtsyConfig {
   apiKey: string;
+  sharedSecret?: string;
   redirectUri: string;
 }
 
@@ -37,11 +38,19 @@ interface EtsyConfig {
 const loadConfig = async (userId: string): Promise<EtsyConfig | null> => {
   const settings = await EtsySettings.findOne({ userId });
   const apiKey = settings?.apiKey || process.env.ETSY_API_KEY;
+  const sharedSecret = settings?.sharedSecret || process.env.ETSY_SHARED_SECRET;
   const redirectUri = settings?.redirectUri || process.env.ETSY_REDIRECT_URI;
   if (!apiKey || !redirectUri) return null;
-  return { apiKey, redirectUri };
+  return { apiKey, sharedSecret, redirectUri };
 };
 
+// Keystring is the OAuth client id; Etsy wants the shared secret in the
+// x-api-key header for API resource calls
+const toCredentials = (config: EtsyConfig) => ({
+  clientId: config.apiKey,
+  apiKeyHeader: config.sharedSecret || config.apiKey,
+});
+
 // Where to send the browser after the OAuth callback: same origin as the
 // redirect URI (the app and API share one domain)
 const settingsUrl = (redirectUri: string | undefined, suffix: string, reason?: string): string => {
@@ -64,9 +73,11 @@ router.get('/config', authenticate, async (req: AuthRequest, res: Response) => {
   try {
     const settings = await EtsySettings.findOne({ userId: req.userId });
     const apiKey = settings?.apiKey || process.env.ETSY_API_KEY;
+    const sharedSecret = settings?.sharedSecret || process.env.ETSY_SHARED_SECRET;
     res.json({
       configured: Boolean(apiKey && (settings?.redirectUri || process.env.ETSY_REDIRECT_URI)),
       apiKeyMasked: apiKey ? maskKey(apiKey) : null,
+      sharedSecretMasked: sharedSecret ? maskKey(sharedSecret) : null,
       redirectUri: settings?.redirectUri || process.env.ETSY_REDIRECT_URI || null,
       source: settings ? 'database' : apiKey ? 'environment' : null,
     });
@@ -77,7 +88,7 @@ router.get('/config', authenticate, async (req: AuthRequest, res: Response) => {
 
 router.put('/config', authenticate, async (req: AuthRequest, res: Response) => {
   try {
-    const { apiKey, redirectUri } = req.body || {};
+    const { apiKey, sharedSecret, redirectUri } = req.body || {};
     if (typeof redirectUri !== 'string' || !redirectUri.trim()) {
       return res.status(400).json({ message: 'redirectUri is required' });
     }
@@ -92,10 +103,14 @@ router.put('/config', authenticate, async (req: AuthRequest, res: Response) => {
     if (!newKey) {
       return res.status(400).json({ message: 'apiKey is required' });
     }
+    const newSecret =
+      typeof sharedSecret === 'string' && sharedSecret.trim()
+        ? sharedSecret.trim()
+        : existing?.sharedSecret;
 
     await EtsySettings.findOneAndUpdate(
       { userId: req.userId },
-      { userId: req.userId, apiKey: newKey, redirectUri: redirectUri.trim() },
+      { userId: req.userId, apiKey: newKey, sharedSecret: newSecret, redirectUri: redirectUri.trim() },
       { upsert: true, new: true, setDefaultsOnInsert: true }
     );
 
@@ -152,7 +167,7 @@ router.get('/callback', async (req: Request, res: Response) => {
     if (!config) throw new Error('Etsy API key is no longer configured');
 
     const tokens = await exchangeCode(config.apiKey, code, pending.verifier, pending.redirectUri);
-    const identity = await fetchIdentity(config.apiKey, tokens.access_token);
+    const identity = await fetchIdentity(toCredentials(config), tokens.access_token);
 
     await EtsyConnection.findOneAndUpdate(
       { userId: pending.userId },
@@ -198,7 +213,7 @@ router.post('/sync', authenticate, async (req: AuthRequest, res: Response) => {
     const config = await loadConfig(req.userId!);
     if (!config) return res.status(400).json({ message: 'Etsy API key is not configured' });
 
-    const result = await syncReceipts(config.apiKey, connection);
+    const result = await syncReceipts(toCredentials(config), connection);
     res.json(result);
   } catch (err: any) {
     console.error('Etsy sync failed:', err);
diff --git a/server/src/services/etsyApi.ts b/server/src/services/etsyApi.ts
index 1cf199f..3bf95aa 100644
--- a/server/src/services/etsyApi.ts
+++ b/server/src/services/etsyApi.ts
@@ -10,6 +10,13 @@ const ETSY_CONNECT_URL = 'https://www.etsy.com/oauth/connect';
 // Read scopes: receipts/transactions, listings, shop info
 export const ETSY_SCOPES = 'transactions_r listings_r shops_r';
 
+// Etsy splits its credentials: the keystring is the OAuth client id, but API
+// resource calls want the app's shared secret in the x-api-key header
+export interface EtsyCredentials {
+  clientId: string;
+  apiKeyHeader: string;
+}
+
 // ---------- OAuth (authorization code + PKCE) ----------
 
 export const generatePkce = () => {
@@ -67,10 +74,10 @@ const refreshTokens = (apiKey: string, refreshToken: string) =>
   });
 
 // Refresh the connection's access token if it expires within the next minute
-const ensureFreshToken = async (apiKey: string, connection: IEtsyConnection): Promise<void> => {
+const ensureFreshToken = async (creds: EtsyCredentials, connection: IEtsyConnection): Promise<void> => {
   if (connection.tokenExpiresAt.getTime() > Date.now() + 60_000) return;
 
-  const tokens = await refreshTokens(apiKey, connection.refreshToken);
+  const tokens = await refreshTokens(creds.clientId, connection.refreshToken);
   connection.accessToken = tokens.access_token;
   connection.refreshToken = tokens.refresh_token;
   connection.tokenExpiresAt = new Date(Date.now() + tokens.expires_in * 1000);
@@ -79,11 +86,11 @@ const ensureFreshToken = async (apiKey: string, connection: IEtsyConnection): Pr
 
 // ---------- API client ----------
 
-const etsyGet = async (apiKey: string, connection: IEtsyConnection, path: string): Promise<any> => {
-  await ensureFreshToken(apiKey, connection);
+const etsyGet = async (creds: EtsyCredentials, connection: IEtsyConnection, path: string): Promise<any> => {
+  await ensureFreshToken(creds, connection);
   const res = await fetch(`${ETSY_API_BASE}${path}`, {
     headers: {
-      'x-api-key': apiKey,
+      'x-api-key': creds.apiKeyHeader,
       Authorization: `Bearer ${connection.accessToken}`,
     },
   });
@@ -100,9 +107,9 @@ export interface EtsyIdentity {
 }
 
 // Resolve the connected user's shop from a fresh access token
-export const fetchIdentity = async (apiKey: string, accessToken: string): Promise<EtsyIdentity> => {
+export const fetchIdentity = async (creds: EtsyCredentials, accessToken: string): Promise<EtsyIdentity> => {
   const res = await fetch(`${ETSY_API_BASE}/application/users/me`, {
-    headers: { 'x-api-key': apiKey, Authorization: `Bearer ${accessToken}` },
+    headers: { 'x-api-key': creds.apiKeyHeader, Authorization: `Bearer ${accessToken}` },
   });
   if (!res.ok) {
     throw new Error(`Etsy users/me failed (${res.status}): ${await res.text()}`);
@@ -115,7 +122,7 @@ export const fetchIdentity = async (apiKey: string, accessToken: string): Promis
   let shopName: string | undefined;
   try {
     const shopRes = await fetch(`${ETSY_API_BASE}/application/shops/${me.shop_id}`, {
-      headers: { 'x-api-key': apiKey, Authorization: `Bearer ${accessToken}` },
+      headers: { 'x-api-key': creds.apiKeyHeader, Authorization: `Bearer ${accessToken}` },
     });
     if (shopRes.ok) {
       const shop: any = await shopRes.json();
@@ -195,7 +202,7 @@ export interface SyncResult {
   receiptsSeen: number;
 }
 
-export const syncReceipts = async (apiKey: string, connection: IEtsyConnection): Promise<SyncResult> => {
+export const syncReceipts = async (creds: EtsyCredentials, connection: IEtsyConnection): Promise<SyncResult> => {
   const products = await Product.find({ userId: connection.userId });
   const result: SyncResult = { created: 0, updated: 0, unmatchedItems: [], receiptsSeen: 0 };
 
@@ -204,7 +211,7 @@ export const syncReceipts = async (apiKey: string, connection: IEtsyConnection):
 
   while (true) {
     const page = await etsyGet(
-      apiKey,
+      creds,
       connection,
       `/application/shops/${connection.shopId}/receipts?limit=${limit}&offset=${offset}`
     );