diff --git a/backend/src/services/apiServer.ts b/backend/src/services/apiServer.ts
index 7b12ba8..61433d6 100644
--- a/backend/src/services/apiServer.ts
+++ b/backend/src/services/apiServer.ts
@@ -133,12 +133,19 @@ const normalizeNewsSymbolsQuery = (value: unknown): string => {
 const getConfiguredFmpApiKey = (): string => {
     const apiKey = config.FMP_API_KEY.trim();
     if (!apiKey || apiKey.toLowerCase() === 'demo') {
-        throw new Error('FMP_API_KEY is required for research and screener endpoints');
+        throw new MissingServiceConfigError('FMP_API_KEY is required for research and screener endpoints');
     }
 
     return apiKey;
 };
 
+class MissingServiceConfigError extends Error {
+    constructor(message: string) {
+        super(message);
+        this.name = 'MissingServiceConfigError';
+    }
+}
+
 interface TradeAuditEvent {
     event: string;
     userId?: string;
@@ -2819,6 +2826,9 @@ RULES:
                 const data = await fetchFmpJson(url) as any;
                 res.json(Array.isArray(data) ? data[0] ?? {} : data);
             } catch (error: any) {
+                if (error instanceof MissingServiceConfigError) {
+                    return res.status(503).json({ error: error.message });
+                }
                 if (error instanceof FmpFetchError) {
                     return res.status(error.status).json({ error: 'FMP profile fetch failed' });
                 }
@@ -2836,6 +2846,9 @@ RULES:
                 const data = await fetchFmpJson(url) as any;
                 res.json(Array.isArray(data) ? data[0] ?? {} : data);
             } catch (error: any) {
+                if (error instanceof MissingServiceConfigError) {
+                    return res.status(503).json({ error: error.message });
+                }
                 if (error instanceof FmpFetchError) {
                     return res.status(error.status).json({ error: 'FMP metrics fetch failed' });
                 }
@@ -2853,6 +2866,9 @@ RULES:
                 const data = await fetchFmpJson(url) as any;
                 res.json({ earnings: Array.isArray(data) ? data : [] });
             } catch (error: any) {
+                if (error instanceof MissingServiceConfigError) {
+                    return res.status(503).json({ error: error.message });
+                }
                 if (error instanceof FmpFetchError) {
                     return res.status(error.status).json({ error: 'FMP earnings fetch failed' });
                 }
@@ -2883,6 +2899,9 @@ RULES:
                 const data = await fetchFmpJson(url) as any;
                 res.json({ results: Array.isArray(data) ? data : [] });
             } catch (error: any) {
+                if (error instanceof MissingServiceConfigError) {
+                    return res.status(503).json({ error: error.message });
+                }
                 if (error instanceof FmpFetchError) {
                     return res.status(error.status).json({ error: 'FMP screener fetch failed' });
                 }