diff --git a/src/App.php b/src/App.php
index abdef4e..d414355 100644
--- a/src/App.php
+++ b/src/App.php
@@ -266,10 +266,14 @@ final class App
         }
 
         $username = (string) ($user['username'] ?? '');
-        $payload = request_json_body();
+        $rawBody = (string) file_get_contents('php://input');
+        $payload = $this->decodeHealthImportPayload($rawBody);
         if ($payload === []) {
-            $this->users->recordHealthImport($username, 'error', 'Leerer oder ungültiger JSON-Import.');
-            json_response(['ok' => false, 'message' => 'Leerer oder ungültiger JSON-Import.'], 400);
+            $traceID = $this->healthImportTraceID();
+            $message = 'Diagnose-ID: ' . $traceID . '. Leerer oder ungültiger JSON-Import.';
+            $this->logHealthImportFailure($traceID, $username, 'Leerer oder ungültiger JSON-Import.', [], strlen($rawBody));
+            $this->users->recordHealthImport($username, 'error', $message);
+            json_response(['ok' => false, 'message' => $message], 400);
         }
 
         try {
@@ -285,11 +289,55 @@ final class App
             $this->users->recordHealthImport($username, 'ok', $message);
             json_response(['ok' => true, 'message' => $message, 'result' => $result]);
         } catch (RuntimeException $exception) {
-            $this->users->recordHealthImport($username, 'error', $exception->getMessage());
-            json_response(['ok' => false, 'message' => $exception->getMessage()], 400);
+            $traceID = $this->healthImportTraceID();
+            $message = 'Diagnose-ID: ' . $traceID . '. ' . $exception->getMessage();
+            $this->logHealthImportFailure($traceID, $username, $exception->getMessage(), $payload, strlen($rawBody));
+            $this->users->recordHealthImport($username, 'error', $message);
+            json_response(['ok' => false, 'message' => $message], 400);
         }
     }
 
+    private function decodeHealthImportPayload(string $rawBody): array
+    {
+        if (trim($rawBody) === '') {
+            return [];
+        }
+
+        $decoded = json_decode($rawBody, true);
+
+        return is_array($decoded) ? $decoded : [];
+    }
+
+    private function healthImportTraceID(): string
+    {
+        try {
+            return substr(bin2hex(random_bytes(4)), 0, 8);
+        } catch (Exception) {
+            return substr(sha1((string) microtime(true)), 0, 8);
+        }
+    }
+
+    private function logHealthImportFailure(string $traceID, string $username, string $message, array $payload, int $rawLength): void
+    {
+        $metrics = $payload === [] ? [] : $this->healthMetricsFromPayload($payload);
+        $workouts = $payload === [] ? [] : $this->healthWorkoutsFromPayload($payload);
+        $context = [
+            'trace_id' => $traceID,
+            'user' => $username,
+            'message' => $message,
+            'method' => (string) ($_SERVER['REQUEST_METHOD'] ?? ''),
+            'path' => (string) ($_SERVER['REQUEST_URI'] ?? ''),
+            'content_type' => (string) ($_SERVER['CONTENT_TYPE'] ?? ($_SERVER['HTTP_CONTENT_TYPE'] ?? '')),
+            'content_length' => (string) ($_SERVER['CONTENT_LENGTH'] ?? ''),
+            'raw_length' => $rawLength,
+            'json_error' => json_last_error_msg(),
+            'user_agent' => (string) ($_SERVER['HTTP_USER_AGENT'] ?? ''),
+            'payload' => $this->healthPayloadDiagnostics($payload, $metrics, $workouts),
+        ];
+
+        error_log('[Mood Health Import] ' . json_encode($context, JSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES));
+    }
+
     private function handleHealthImportStatus(): void
     {
         $user = $this->requireUser();
@@ -569,6 +617,106 @@ final class App
         return implode('. ', $parts) . '.';
     }
 
+    private function healthPayloadDiagnostics(array $payload, array $metrics, array $workouts): array
+    {
+        return [
+            'top_level' => $this->describeHealthPayloadNode($payload),
+            'metrics_count' => count($metrics),
+            'workouts_count' => count($workouts),
+            'metric_samples' => $this->healthMetricDiagnostics($metrics),
+            'workout_samples' => $this->healthArraySamples($workouts),
+            'payload_samples' => $this->healthNestedArraySamples($payload),
+        ];
+    }
+
+    private function healthMetricDiagnostics(array $metrics): array
+    {
+        $samples = [];
+        foreach (array_slice($metrics, 0, 8) as $index => $metric) {
+            if (!is_array($metric)) {
+                continue;
+            }
+
+            $data = is_array($metric['data'] ?? null) ? $metric['data'] : [];
+            $firstPoint = null;
+            foreach ($data as $point) {
+                if (is_array($point)) {
+                    $firstPoint = $point;
+                    break;
+                }
+            }
+
+            $samples[] = [
+                'index' => $index,
+                'name' => (string) ($metric['name'] ?? ''),
+                'normalized' => $this->healthMetricName((string) ($metric['name'] ?? '')),
+                'data_count' => count($data),
+                'keys' => array_slice(array_keys($metric), 0, 12),
+                'first_point' => is_array($firstPoint) ? $this->describeHealthPayloadNode($firstPoint) : null,
+            ];
+        }
+
+        return $samples;
+    }
+
+    private function healthArraySamples(array $items): array
+    {
+        $samples = [];
+        foreach (array_slice($items, 0, 5) as $index => $item) {
+            if (is_array($item)) {
+                $samples[] = ['index' => $index] + $this->describeHealthPayloadNode($item);
+            }
+        }
+
+        return $samples;
+    }
+
+    private function healthNestedArraySamples(array $payload, string $path = '$', int $depth = 0): array
+    {
+        if ($depth > 2) {
+            return [];
+        }
+
+        $samples = [];
+        foreach ($payload as $key => $value) {
+            $currentPath = $path . (is_int($key) ? '[' . $key . ']' : '.' . (string) $key);
+            if (!is_array($value)) {
+                continue;
+            }
+
+            $samples[] = ['path' => $currentPath] + $this->describeHealthPayloadNode($value);
+            if (count($samples) >= 12) {
+                break;
+            }
+
+            foreach ($this->healthNestedArraySamples($value, $currentPath, $depth + 1) as $nested) {
+                $samples[] = $nested;
+                if (count($samples) >= 12) {
+                    break 2;
+                }
+            }
+        }
+
+        return $samples;
+    }
+
+    private function describeHealthPayloadNode(array $node): array
+    {
+        $keys = array_slice(array_keys($node), 0, 12);
+        $types = [];
+        foreach ($keys as $key) {
+            $value = $node[$key] ?? null;
+            $types[(string) $key] = is_array($value) ? 'array(' . count($value) . ')' : get_debug_type($value);
+        }
+
+        return [
+            'is_list' => array_is_list($node),
+            'count' => count($node),
+            'keys' => $keys,
+            'types' => $types,
+        ];
+    }
+
     private function healthEventsFromMetrics(array $metrics): array
     {
         $steps = [];