diff --git a/src/lib/client/appointment-crypto.ts b/src/lib/client/appointment-crypto.ts
index 92d20e2..fdb524f 100644
--- a/src/lib/client/appointment-crypto.ts
+++ b/src/lib/client/appointment-crypto.ts
@@ -205,10 +205,14 @@ export class UnifiedAppointmentCrypto {
       if (!challengeResponse.ok) {
         if (challengeResponse.status === 429) {
           const errorData = await challengeResponse.json();
-          const retryAfterSeconds = Math.ceil((errorData.retryAfterMs || 0) / 1000);
-          throw new Error(
-            `Too many failed attempts. Please try again in ${retryAfterSeconds} seconds.`,
-          );
+          const retryAfterSeconds = Math.ceil((errorData.retryAfterMs || 60000) / 1000);
+          if (retryAfterSeconds > 0) {
+            throw new Error(
+              `Too many failed attempts. Please try again in ${retryAfterSeconds} seconds.`,
+            );
+          } else {
+            throw new Error("Too many failed attempts. Please try again later.");
+          }
         }
         throw new Error("Challenge could not be retrieved");
       }
@@ -240,11 +244,15 @@ export class UnifiedAppointmentCrypto {
       if (!verificationResponse.ok) {
         const errorData = await verificationResponse.json();
         console.error("❌ Challenge verification failed:", errorData);
-        if (verificationResponse.status === 429 && errorData.retryAfterMs) {
-          const retryAfterSeconds = Math.ceil(errorData.retryAfterMs / 1000);
-          throw new Error(
-            `Too many failed attempts. Please try again in ${retryAfterSeconds} seconds.`,
-          );
+        if (verificationResponse.status === 429) {
+          const retryAfterSeconds = Math.ceil((errorData.retryAfterMs || 60000) / 1000);
+          if (retryAfterSeconds > 0) {
+            throw new Error(
+              `Too many failed attempts. Please try again in ${retryAfterSeconds} seconds.`,
+            );
+          } else {
+            throw new Error("Too many failed attempts. Please try again later.");
+          }
         }
         throw new Error("Challenge verification failed");
       }
diff --git a/src/lib/server/services/challenge-throttle.ts b/src/lib/server/services/challenge-throttle.ts
index 3ad3e8e..c1fdd88 100644
--- a/src/lib/server/services/challenge-throttle.ts
+++ b/src/lib/server/services/challenge-throttle.ts
@@ -20,11 +20,17 @@ interface ThrottleResult {
   failedAttempts: number;
 }
 
+// Throttle reset duration: 1 hour
+const THROTTLE_RESET_DURATION_MS = 60 * 60 * 1000;
+
 /**
- * Calculate exponential backoff delay for PIN challenges
- * First 2 retries: wait for a few seconds
- * Third retry: wait for one minute
- * Scale up to thirty minutes
+ * Calculate escalating delay for PIN challenges
+ * Uses a fixed escalation pattern that increases with each failed attempt:
+ * - 1st failure: 2 seconds
+ * - 2nd failure: 10 seconds
+ * - 3rd failure: 1 minute
+ * - 4th failure: 5 minutes
+ * - 5+ failures: 30 minutes
  */
 function calculatePinThrottleDelay(failedAttempts: number): number {
   if (failedAttempts === 0) return 0;
@@ -184,7 +190,7 @@ class ChallengeThrottleService {
 
       if (records.length === 0) {
         // Create new throttle record
-        const resetAt = new Date(now.getTime() + 60 * 60 * 1000); // 1 hour from now
+        const resetAt = new Date(now.getTime() + THROTTLE_RESET_DURATION_MS);
         await db.insert(challengeThrottle).values({
           id: identifier,
           failedAttempts: 1,
@@ -219,7 +225,7 @@ class ChallengeThrottleService {
 
       if (records.length === 0) {
         // Create new throttle record
-        const resetAt = new Date(now.getTime() + 60 * 60 * 1000); // 1 hour from now
+        const resetAt = new Date(now.getTime() + THROTTLE_RESET_DURATION_MS);
         await db.insert(passkeyChallengeThrottle).values({
           id: identifier,
           failedAttempts: 1,
diff --git a/src/lib/utils/passkey.ts b/src/lib/utils/passkey.ts
index 242fdc0..9b00faf 100644
--- a/src/lib/utils/passkey.ts
+++ b/src/lib/utils/passkey.ts
@@ -49,34 +49,39 @@ export const fetchChallenge = async (email: string) => {
     body: JSON.stringify({ email }),
   });
 
+  let data;
   try {
-    const data = await resp.json();
+    data = await resp.json();
+  } catch (error) {
+    logger.error("Failed to parse challenge response", { email, error });
+    return null;
+  }
 
-    // Handle throttling
-    if (resp.status === 429) {
-      const retryAfterSeconds = Math.ceil((data.retryAfterMs || 60000) / 1000);
-      logger.error("Challenge request throttled", {
-        email,
-        retryAfterSeconds,
-      });
+  // Handle throttling
+  if (resp.status === 429) {
+    const retryAfterSeconds = Math.ceil((data.retryAfterMs || 60000) / 1000);
+    logger.error("Challenge request throttled", {
+      email,
+      retryAfterSeconds,
+    });
+    if (retryAfterSeconds > 0) {
       throw new Error(
         `Too many failed attempts. Please try again in ${retryAfterSeconds} seconds.`,
       );
+    } else {
+      throw new Error("Too many failed attempts. Please try again later.");
     }
-
-    if (!resp.ok) {
-      logger.error("Failed to fetch challenge", { email, status: resp.status });
-      return null;
-    }
-
-    return {
-      id: data.rpId,
-      challenge: data.challenge,
-    };
-  } catch (error) {
-    logger.error("Failed to fetch challenge", { email, status: resp.status, error });
-    throw error;
   }
+
+  if (!resp.ok) {
+    logger.error("Failed to fetch challenge", { email, status: resp.status });
+    return null;
+  }
+
+  return {
+    id: data.rpId,
+    challenge: data.challenge,
+  };
 };
 
 export const getCredentialOptions = ({