diff --git a/src/Http/MunicipalParametersClient.php b/src/Http/MunicipalParametersClient.php
index ad838d9..8553c82 100644
--- a/src/Http/MunicipalParametersClient.php
+++ b/src/Http/MunicipalParametersClient.php
@@ -148,7 +148,7 @@ private function serviceCode(string $codigoServico): string
 
         if (preg_match('/^\\d{9}$/', $value) !== 1) {
             throw new \InvalidArgumentException(
-                'Municipal parameters service code must be a 9-digit NBS code.',
+                'Municipal parameters service code must contain exactly 9 digits (6-digit national service code plus 3-digit municipal subdivision, or 000 when there is no subdivision).',
             );
         }
 
diff --git a/tests/Unit/Http/MunicipalParametersClientTest.php b/tests/Unit/Http/MunicipalParametersClientTest.php
index 4a3b15a..9f483cf 100644
--- a/tests/Unit/Http/MunicipalParametersClientTest.php
+++ b/tests/Unit/Http/MunicipalParametersClientTest.php
@@ -50,15 +50,15 @@ public function testConvenioUsesOfficialPath(): void
     public function testAliquotaNormalizesServiceCodeAndPreservesCompetence(): void
     {
         self::$server->setResponseOfPath(
-            '/parametrizacao/3303302/115022000/2026-10-03/aliquota',
+            '/parametrizacao/3303302/010101000/2026-10-03/aliquota',
             new Response('{"aliquotas":[{"Aliq":5.0}]}', ['Content-Type' => 'application/json'], 200),
         );
 
-        $result = $this->client()->aliquota('3303302', '1.1502.20.00', '2026-10-03');
+        $result = $this->client()->aliquota('3303302', '01.01.01.000', '2026-10-03');
 
         self::assertSame(5.0, $result['aliquotas'][0]['Aliq'] ?? null);
         self::assertSame(
-            '/parametrizacao/3303302/115022000/2026-10-03/aliquota',
+            '/parametrizacao/3303302/010101000/2026-10-03/aliquota',
             self::$server->getLastRequest()?->getRequestUri(),
         );
     }
@@ -66,12 +66,12 @@ public function testAliquotaNormalizesServiceCodeAndPreservesCompetence(): void
     public function testRegimesRetencoesAndBenefitUseOfficialPaths(): void
     {
         self::$server->setResponseOfPath(
-            '/parametrizacao/3303302/115022000/2026-10-03/regimes_especiais',
+            '/parametrizacao/3303302/010101000/2026-10-03/regimes_especiais',
             new Response('{"regimes":[]}', ['Content-Type' => 'application/json'], 200),
         );
-        $this->client()->regimesEspeciais('3303302', '115022000', '2026-10-03');
+        $this->client()->regimesEspeciais('3303302', '010101000', '2026-10-03');
         self::assertSame(
-            '/parametrizacao/3303302/115022000/2026-10-03/regimes_especiais',
+            '/parametrizacao/3303302/010101000/2026-10-03/regimes_especiais',
             self::$server->getLastRequest()?->getRequestUri(),
         );