diff --git a/km4k2/card_sdk.py b/km4k2/card_sdk.py
index 79a84ad..d75c692 100644
--- a/km4k2/card_sdk.py
+++ b/km4k2/card_sdk.py
@@ -13,21 +13,23 @@ def __init__(self, base_url: str, api_key: str) -> None:
         self.api_key = api_key
 
     def verify(self, idm: str) -> bool:
+        """
+        Raises:
+            requests.exceptions.HTTPError: if API returns unexpected HTTP status
+            requests.exceptions.JSONDecodeError: if API returns invalid JSON
+        """
         url = urljoin(self.base_url, "/api/card/verify")
         payload = json.dumps({"idm": idm})
         headers = {"X-Api-Key": self.api_key, "Content-Type": "application/json"}
         response = requests.request("GET", url, headers=headers, data=payload)
 
-        try:
-            response.raise_for_status()
-        except requests.exceptions.HTTPError as e:
-            print(e)
+        if response.status_code == requests.codes.not_found:  # unregistered
             return False
-
-        try:
-            status = response.json()
-        except requests.exceptions.JSONDecodeError as e:
-            print(e)
+        if response.status_code == requests.codes.forbidden:  # expired
             return False
 
-        return status["verified"] is not None and status["verified"]
+        response.raise_for_status()
+
+        # ok
+        status = response.json()
+        return status["verified"]
diff --git a/km4k2/km4k.py b/km4k2/km4k.py
index 5814978..a6a6cef 100644
--- a/km4k2/km4k.py
+++ b/km4k2/km4k.py
@@ -25,7 +25,14 @@ def start_system(isopen, okled_pin, ngled_pin, verifier: CardVerifierInterface):
     while True:
         idm = read_nfc()
         if idm:
-            verified = verifier.verify(idm.decode())
+            try:
+                verified = verifier.verify(idm.decode())
+            except Exception as e:  # noqa: BLE001
+                GPIO.output(ngled_pin, GPIO.HIGH)
+                time.sleep(3)
+                GPIO.output(ngled_pin, GPIO.LOW)
+                print(e)
+                continue
             if verified:
                 print("Registered (idm:" + idm.decode() + ")")