diff --git a/bootstrap/middlewares.php b/bootstrap/middlewares.php
index 5b7fb89..00a0dd9 100644
--- a/bootstrap/middlewares.php
+++ b/bootstrap/middlewares.php
@@ -4,11 +4,14 @@ declare(strict_types=1);
 
 use Illuminate\Foundation\Configuration\Middleware;
 use Presentation\Api\V1\Http\Middlewares\EnsureApiV1AcceptsJson;
+use Presentation\Api\V1\Http\Middlewares\NormalizeQueryStringArrays;
 use Presentation\Api\V1\Http\Middlewares\SetApiV1Etag;
 use Presentation\Api\V1\Http\Middlewares\TransformApiV1Response;
 use Presentation\Api\V1\Http\Middlewares\VerifyHmacSignature;
 
 return function (Middleware $middleware): void {
+    $middleware->prepend(NormalizeQueryStringArrays::class);
+
     $middleware->alias([
         'auth.hmac' => VerifyHmacSignature::class,
     ]);
diff --git a/src/Presentation/Api/V1/Http/Middlewares/NormalizeQueryStringArrays.php b/src/Presentation/Api/V1/Http/Middlewares/NormalizeQueryStringArrays.php
new file mode 100644
index 0000000..d64abf3
--- /dev/null
+++ b/src/Presentation/Api/V1/Http/Middlewares/NormalizeQueryStringArrays.php
@@ -0,0 +1,103 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Presentation\Api\V1\Http\Middlewares;
+
+use Illuminate\Http\Request;
+use Symfony\Component\HttpFoundation\Response;
+
+final class NormalizeQueryStringArrays
+{
+    /**
+     * Query parameters expected to be arrays in API V1.
+     *
+     * @var list<string>
+     */
+    private const ARRAY_QUERY_PARAMS = [
+        'brands',
+        'siteIds',
+    ];
+
+    /**
+     * @param  \Closure(Request): Response  $next
+     */
+    public function handle(Request $request, \Closure $next): Response
+    {
+        if (! $request->is('api/*')) {
+            /** @var Response */
+            return $next($request);
+        }
+
+        $queryString = $request->server->get('QUERY_STRING');
+
+        if (is_string($queryString) && $queryString !== '') {
+            $normalized = $this->parseQueryString($queryString);
+
+            if (! empty($normalized)) {
+                $request->query->replace(array_merge($request->query->all(), $normalized));
+            }
+        }
+
+        /** @var Response */
+        return $next($request);
+    }
+
+    /**
+     * Parse raw query string while properly aggregating repeated keys,
+     * bracket keys (e.g. siteIds[]=A), and known array parameters into PHP arrays.
+     *
+     * @return array<string, mixed>
+     */
+    private function parseQueryString(string $queryString): array
+    {
+        $pairs  = explode('&', $queryString);
+        $result = [];
+
+        foreach ($pairs as $pair) {
+            if ($pair === '') {
+                continue;
+            }
+
+            $parts  = explode('=', $pair, 2);
+            $rawKey = urldecode($parts[0]);
+            $value  = isset($parts[1]) ? urldecode($parts[1]) : '';
+
+            // Strip trailing empty brackets: 'brands[]' -> 'brands'
+            if (str_ends_with($rawKey, '[]')) {
+                $key = substr($rawKey, 0, -2);
+                if (! isset($result[$key]) || ! is_array($result[$key])) {
+                    $result[$key] = [];
+                }
+                $result[$key][] = $value;
+            } elseif (isset($result[$rawKey])) {
+                // Repeated parameter: 'siteIds=A&siteIds=B'
+                if (! is_array($result[$rawKey])) {
+                    $result[$rawKey] = [$result[$rawKey]];
+                }
+                $result[$rawKey][] = $value;
+            } else {
+                $result[$rawKey] = $value;
+            }
+        }
+
+        // For known array parameters, normalize single scalars or comma-separated lists into arrays
+        foreach (self::ARRAY_QUERY_PARAMS as $arrayParam) {
+            if (isset($result[$arrayParam])) {
+                $val = $result[$arrayParam];
+                if (is_string($val)) {
+                    if (str_contains($val, ',')) {
+                        $result[$arrayParam] = array_values(array_filter(
+                            explode(',', $val),
+                            static fn (string $item): bool => $item !== ''
+                        ));
+                    } else {
+                        $result[$arrayParam] = [$val];
+                    }
+                }
+            }
+        }
+
+        return $result;
+    }
+}
diff --git a/tests/Feature/Api/V1/Middlewares/NormalizeQueryStringArraysTest.php b/tests/Feature/Api/V1/Middlewares/NormalizeQueryStringArraysTest.php
new file mode 100644
index 0000000..181d12a
--- /dev/null
+++ b/tests/Feature/Api/V1/Middlewares/NormalizeQueryStringArraysTest.php
@@ -0,0 +1,92 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Feature\Api\V1\Middlewares;
+
+use Illuminate\Http\Request;
+use Presentation\Api\V1\Http\Middlewares\NormalizeQueryStringArrays;
+use Symfony\Component\HttpFoundation\Response;
+
+describe('NormalizeQueryStringArrays Middleware Feature Tests', function (): void {
+    it('normalizes repeated query parameters into array', function (): void {
+        // GIVEN
+        $middleware = new NormalizeQueryStringArrays();
+        $request    = Request::create('/api/v1/employees?siteIds=LDCSER&siteIds=SLELA', 'GET');
+
+        // WHEN
+        $response = $middleware->handle($request, function (Request $req): Response {
+            expect($req->query('siteIds'))->toBe(['LDCSER', 'SLELA']);
+
+            return new Response();
+        });
+
+        // THEN
+        expect($response->getStatusCode())->toBe(200);
+    });
+
+    it('normalizes bracket query parameters into array without trailing brackets in key', function (): void {
+        // GIVEN
+        $middleware = new NormalizeQueryStringArrays();
+        $request    = Request::create('/api/v1/employees?siteIds[]=LDCSER&siteIds[]=SLELA', 'GET');
+
+        // WHEN
+        $response = $middleware->handle($request, function (Request $req): Response {
+            expect($req->query('siteIds'))->toBe(['LDCSER', 'SLELA']);
+
+            return new Response();
+        });
+
+        // THEN
+        expect($response->getStatusCode())->toBe(200);
+    });
+
+    it('normalizes single scalar brand query parameter into array', function (): void {
+        // GIVEN
+        $middleware = new NormalizeQueryStringArrays();
+        $request    = Request::create('/api/v1/inco-sheets?brands=LGL01', 'GET');
+
+        // WHEN
+        $response = $middleware->handle($request, function (Request $req): Response {
+            expect($req->query('brands'))->toBe(['LGL01']);
+
+            return new Response();
+        });
+
+        // THEN
+        expect($response->getStatusCode())->toBe(200);
+    });
+
+    it('normalizes comma separated brands into array', function (): void {
+        // GIVEN
+        $middleware = new NormalizeQueryStringArrays();
+        $request    = Request::create('/api/v1/inco-sheets?brands=LGL01,MCQ01', 'GET');
+
+        // WHEN
+        $response = $middleware->handle($request, function (Request $req): Response {
+            expect($req->query('brands'))->toBe(['LGL01', 'MCQ01']);
+
+            return new Response();
+        });
+
+        // THEN
+        expect($response->getStatusCode())->toBe(200);
+    });
+
+    it('bypasses non-api routes', function (): void {
+        // GIVEN
+        $middleware = new NormalizeQueryStringArrays();
+        $request    = Request::create('/ping?siteIds=LDCSER&siteIds=SLELA', 'GET');
+
+        // WHEN
+        $response = $middleware->handle($request, function (Request $req): Response {
+            // PHP native behavior: last value wins if not normalized
+            expect($req->query('siteIds'))->toBe('SLELA');
+
+            return new Response();
+        });
+
+        // THEN
+        expect($response->getStatusCode())->toBe(200);
+    });
+});