diff --git a/src/neptune_scale/net/api_client.py b/src/neptune_scale/net/api_client.py
index 1bbcccf..bd0bcc8 100644
--- a/src/neptune_scale/net/api_client.py
+++ b/src/neptune_scale/net/api_client.py
@@ -75,8 +75,10 @@
 from neptune_scale.exceptions import (
     NeptuneConnectionLostError,
     NeptuneInvalidCredentialsError,
+    NeptuneScaleError,
     NeptuneUnableToAuthenticateError,
 )
+from neptune_scale.net.util import raise_for_http_status
 from neptune_scale.sync.parameters import REQUEST_TIMEOUT
 from neptune_scale.util.abstract import Resource
 from neptune_scale.util.envs import ALLOW_SELF_SIGNED_CERTIFICATE
@@ -106,11 +108,25 @@ def get_config_and_token_urls(
         verify_ssl=verify_ssl,
         timeout=Timeout(timeout=REQUEST_TIMEOUT),
     ) as client:
-        config = get_client_config.sync(client=client)
-        if config is None or isinstance(config, Error):
-            raise RuntimeError(f"Failed to get client config: {config}")
-        response = client.get_httpx_client().get(config.security.open_id_discovery)
-        token_urls = TokenRefreshingURLs.from_dict(response.json())
+        response = get_client_config.sync_detailed(client=client)
+        if response.parsed is None:
+            raise NeptuneScaleError(
+                message="Failed to initialize API client: invalid response from server. "
+                f"Status code={response.status_code}"
+            )
+
+        if response.status_code != 200 or not isinstance(response.parsed, ClientConfig):
+            error = response.parsed if isinstance(response.parsed, Error) else None
+
+            if response.status_code == 400 and error and isinstance(error.message, str):
+                if "X-Neptune-Api-Token" in error.message:
+                    raise NeptuneInvalidCredentialsError()
+
+            raise_for_http_status(response.status_code)
+
+        config = cast(ClientConfig, response.parsed)
+        token_data = client.get_httpx_client().get(config.security.open_id_discovery)
+        token_urls = TokenRefreshingURLs.from_dict(token_data.json())
     return config, token_urls
 
 
@@ -144,7 +160,10 @@ def search_entries(
 
 class HostedApiClient(ApiClient):
     def __init__(self, api_token: str) -> None:
-        credentials = Credentials.from_api_key(api_key=api_token)
+        try:
+            credentials = Credentials.from_api_key(api_key=api_token)
+        except InvalidApiTokenException:
+            raise NeptuneInvalidCredentialsError()
 
         verify_ssl: bool = os.environ.get(ALLOW_SELF_SIGNED_CERTIFICATE, "False").lower() in ("false", "0")
 
diff --git a/src/neptune_scale/net/util.py b/src/neptune_scale/net/util.py
index beca024..21ed111 100644
--- a/src/neptune_scale/net/util.py
+++ b/src/neptune_scale/net/util.py
@@ -13,6 +13,17 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from neptune_scale.exceptions import (
+    NeptuneConnectionLostError,
+    NeptuneInternalServerError,
+    NeptuneTooManyRequestsResponseError,
+    NeptuneUnauthorizedError,
+    NeptuneUnexpectedResponseError,
+)
+from neptune_scale.util import get_logger
+
+logger = get_logger()
+
 
 def escape_nql_criterion(criterion: str) -> str:
     """
@@ -20,3 +31,19 @@ def escape_nql_criterion(criterion: str) -> str:
     """
 
     return criterion.replace("\\", r"\\").replace('"', r"\"")
+
+
+def raise_for_http_status(status_code: int) -> None:
+    assert status_code >= 400, f"Status code {status_code} is not an error"
+
+    logger.error("HTTP response error: %s", status_code)
+    if status_code == 403:
+        raise NeptuneUnauthorizedError()
+    elif status_code == 408:
+        raise NeptuneConnectionLostError()
+    elif status_code == 429:
+        raise NeptuneTooManyRequestsResponseError()
+    elif status_code // 100 == 5:
+        raise NeptuneInternalServerError()
+    else:
+        raise NeptuneUnexpectedResponseError()
diff --git a/src/neptune_scale/sync/sync_process.py b/src/neptune_scale/sync/sync_process.py
index e68c7ab..f7c165f 100644
--- a/src/neptune_scale/sync/sync_process.py
+++ b/src/neptune_scale/sync/sync_process.py
@@ -54,7 +54,6 @@
     NeptuneAttributeTypeUnsupported,
     NeptuneConnectionLostError,
     NeptuneFloatValueNanInfUnsupported,
-    NeptuneInternalServerError,
     NeptuneProjectInvalidName,
     NeptuneProjectNotFound,
     NeptuneRetryableError,
@@ -70,16 +69,14 @@
     NeptuneStringSetExceedsSizeLimit,
     NeptuneStringValueExceedsSizeLimit,
     NeptuneSynchronizationStopped,
-    NeptuneTooManyRequestsResponseError,
-    NeptuneUnauthorizedError,
     NeptuneUnexpectedError,
-    NeptuneUnexpectedResponseError,
 )
 from neptune_scale.net.api_client import (
     ApiClient,
     backend_factory,
     with_api_errors_handling,
 )
+from neptune_scale.net.util import raise_for_http_status
 from neptune_scale.sync.aggregating_queue import AggregatingQueue
 from neptune_scale.sync.errors_tracking import ErrorsQueue
 from neptune_scale.sync.parameters import (
@@ -438,7 +435,7 @@ def submit(self, *, operation: RunOperation) -> Optional[SubmitResponse]:
 
         status_code = response.status_code
         if status_code != 200:
-            _raise_exception(status_code)
+            raise_for_http_status(status_code)
 
         return response.parsed
 
@@ -482,20 +479,6 @@ def work(self) -> None:
             raise NeptuneSynchronizationStopped() from e
 
 
-def _raise_exception(status_code: int) -> None:
-    logger.error("HTTP response error: %s", status_code)
-    if status_code == 403:
-        raise NeptuneUnauthorizedError()
-    elif status_code == 408:
-        raise NeptuneConnectionLostError()
-    elif status_code == 429:
-        raise NeptuneTooManyRequestsResponseError()
-    elif status_code // 100 == 5:
-        raise NeptuneInternalServerError()
-    else:
-        raise NeptuneUnexpectedResponseError()
-
-
 class StatusTrackingThread(Daemon, WithResources):
     def __init__(
         self,
@@ -542,7 +525,7 @@ def check_batch(self, *, request_ids: list[str]) -> Optional[BulkRequestStatus]:
         status_code = response.status_code
 
         if status_code != 200:
-            _raise_exception(status_code)
+            raise_for_http_status(status_code)
 
         return response.parsed