diff --git a/client/src/pages/Settings.tsx b/client/src/pages/Settings.tsx
index 63adfbe..b1a4436 100644
--- a/client/src/pages/Settings.tsx
+++ b/client/src/pages/Settings.tsx
@@ -51,7 +51,11 @@ const Settings = () => {
       toast.success('Etsy shop connected!');
       window.history.replaceState({}, '', window.location.pathname);
     } else if (etsyResult === 'error') {
-      toast.error('Etsy connection failed. Please try again.');
+      const reason = params.get('reason');
+      toast.error(
+        reason ? `Etsy connection failed: ${reason}` : 'Etsy connection failed. Please try again.',
+        { duration: 12000 }
+      );
       window.history.replaceState({}, '', window.location.pathname);
     }
   }, []);
diff --git a/server/src/routes/etsy.ts b/server/src/routes/etsy.ts
index c06cd66..86de0b7 100644
--- a/server/src/routes/etsy.ts
+++ b/server/src/routes/etsy.ts
@@ -44,14 +44,15 @@ const loadConfig = async (userId: string): Promise<EtsyConfig | null> => {
 
 // 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): string => {
+const settingsUrl = (redirectUri: string | undefined, suffix: string, reason?: string): string => {
   let origin = process.env.CLIENT_URL || 'http://localhost:3000';
   try {
     if (redirectUri) origin = new URL(redirectUri).origin;
   } catch {
     // keep fallback
   }
-  return `${origin}/settings?etsy=${suffix}`;
+  const reasonParam = reason ? `&reason=${encodeURIComponent(reason.slice(0, 300))}` : '';
+  return `${origin}/settings?etsy=${suffix}${reasonParam}`;
 };
 
 const maskKey = (key: string): string =>
@@ -137,7 +138,12 @@ router.get('/callback', async (req: Request, res: Response) => {
   const pending = typeof state === 'string' ? pendingAuth.get(state) : undefined;
 
   if (error || typeof code !== 'string' || !pending) {
-    return res.redirect(settingsUrl(pending?.redirectUri, 'error'));
+    const reason = error
+      ? `Etsy returned: ${error}${req.query.error_description ? ` — ${req.query.error_description}` : ''}`
+      : !pending
+        ? 'Login attempt expired or unknown (possibly a server restart) — try connecting again'
+        : 'No authorization code returned';
+    return res.redirect(settingsUrl(pending?.redirectUri, 'error', reason));
   }
   pendingAuth.delete(String(state));
 
@@ -163,9 +169,9 @@ router.get('/callback', async (req: Request, res: Response) => {
     );
 
     res.redirect(settingsUrl(pending.redirectUri, 'connected'));
-  } catch (err) {
+  } catch (err: any) {
     console.error('Etsy OAuth callback failed:', err);
-    res.redirect(settingsUrl(pending.redirectUri, 'error'));
+    res.redirect(settingsUrl(pending.redirectUri, 'error', err?.message || 'Token exchange failed'));
   }
 });
 
diff --git a/server/src/services/etsyApi.ts b/server/src/services/etsyApi.ts
index 272111e..1cf199f 100644
--- a/server/src/services/etsyApi.ts
+++ b/server/src/services/etsyApi.ts
@@ -38,10 +38,11 @@ interface TokenResponse {
 }
 
 const requestToken = async (body: Record<string, string>): Promise<TokenResponse> => {
+  // OAuth 2.0 token endpoints take form-encoded bodies (RFC 6749)
   const res = await fetch(ETSY_TOKEN_URL, {
     method: 'POST',
-    headers: { 'Content-Type': 'application/json' },
-    body: JSON.stringify(body),
+    headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
+    body: new URLSearchParams(body).toString(),
   });
   if (!res.ok) {
     throw new Error(`Etsy token request failed (${res.status}): ${await res.text()}`);