diff --git a/gnosis/safe/api/base_api.py b/gnosis/safe/api/base_api.py
index 54da7aa9d..9bc4a3871 100644
--- a/gnosis/safe/api/base_api.py
+++ b/gnosis/safe/api/base_api.py
@@ -4,7 +4,11 @@
 
 import requests
 
-from gnosis.eth.ethereum_client import EthereumClient, EthereumNetwork
+from gnosis.eth.ethereum_client import (
+    EthereumClient,
+    EthereumNetwork,
+    EthereumNetworkNotSupported,
+)
 
 
 class SafeAPIException(Exception):
@@ -15,19 +19,27 @@ class SafeBaseAPI(ABC):
     URL_BY_NETWORK: Dict[EthereumNetwork, str] = {}
 
     def __init__(
-        self, network: EthereumNetwork, ethereum_client: Optional[EthereumClient] = None
+        self,
+        network: EthereumNetwork,
+        ethereum_client: Optional[EthereumClient] = None,
+        base_url: Optional[str] = None,
     ):
+        """
+        :param network: Network for the transaction service
+        :param ethereum_client:
+        :param base_url: If a custom transaction service is used
+        :raises: EthereumNetworkNotSupported
+        """
         self.network = network
         self.ethereum_client = ethereum_client
-        self.base_url = self.URL_BY_NETWORK[network]
+        self.base_url = base_url or self.URL_BY_NETWORK.get(network)
+        if not self.base_url:
+            raise EthereumNetworkNotSupported(network)
 
     @classmethod
-    def from_ethereum_client(
-        cls, ethereum_client: EthereumClient
-    ) -> Optional["SafeBaseAPI"]:
+    def from_ethereum_client(cls, ethereum_client: EthereumClient) -> "SafeBaseAPI":
         ethereum_network = ethereum_client.get_network()
-        if ethereum_network in cls.URL_BY_NETWORK:
-            return cls(ethereum_network, ethereum_client=ethereum_client)
+        return cls(ethereum_network, ethereum_client=ethereum_client)
 
     def _get_request(self, url: str) -> requests.Response:
         full_url = urljoin(self.base_url, url)
diff --git a/gnosis/safe/api/transaction_service_api.py b/gnosis/safe/api/transaction_service_api.py
index 4e7ee58f7..54886922e 100644
--- a/gnosis/safe/api/transaction_service_api.py
+++ b/gnosis/safe/api/transaction_service_api.py
@@ -19,14 +19,14 @@
 class TransactionServiceApi(SafeBaseAPI):
     URL_BY_NETWORK = {
         EthereumNetwork.ARBITRUM: "https://safe-transaction.arbitrum.gnosis.io",
-        EthereumNetwork.AURORA: "https://safe-transaction.aurora.gnosis.io/",
+        EthereumNetwork.AURORA: "https://safe-transaction.aurora.gnosis.io",
         EthereumNetwork.AVALANCHE: "https://safe-transaction.avalanche.gnosis.io",
         EthereumNetwork.BINANCE: "https://safe-transaction.bsc.gnosis.io",
         EthereumNetwork.ENERGY_WEB_CHAIN: "https://safe-transaction.ewc.gnosis.io",
         EthereumNetwork.GOERLI: "https://safe-transaction.goerli.gnosis.io",
         EthereumNetwork.MAINNET: "https://safe-transaction.mainnet.gnosis.io",
         EthereumNetwork.MATIC: "https://safe-transaction.polygon.gnosis.io",
-        EthereumNetwork.OPTIMISTIC: "https://safe-transaction.optimism.gnosis.io/",
+        EthereumNetwork.OPTIMISTIC: "https://safe-transaction.optimism.gnosis.io",
         EthereumNetwork.RINKEBY: "https://safe-transaction.rinkeby.gnosis.io",
         EthereumNetwork.VOLTA: "https://safe-transaction.volta.gnosis.io",
         EthereumNetwork.XDAI: "https://safe-transaction.xdai.gnosis.io",
diff --git a/gnosis/safe/tests/api/test_transaction_service_api.py b/gnosis/safe/tests/api/test_transaction_service_api.py
index 8cfaa6501..1f05ac36f 100644
--- a/gnosis/safe/tests/api/test_transaction_service_api.py
+++ b/gnosis/safe/tests/api/test_transaction_service_api.py
@@ -1,18 +1,45 @@
-import unittest
+from unittest import mock
 
-from gnosis.eth import EthereumNetwork
+from django.test import TestCase
+
+from gnosis.eth import EthereumClient, EthereumNetwork, EthereumNetworkNotSupported
 from gnosis.eth.tests.ethereum_test_case import EthereumTestCaseMixin
 
 from ...api.transaction_service_api import TransactionServiceApi
 
 
-class TestTransactionServiceAPI(EthereumTestCaseMixin, unittest.TestCase):
+class TestTransactionServiceAPI(EthereumTestCaseMixin, TestCase):
     def setUp(self) -> None:
-        self.transaction_service = TransactionServiceApi(
+        self.transaction_service_api = TransactionServiceApi(
             EthereumNetwork.RINKEBY, ethereum_client=self.ethereum_client
         )
         self.safe_address = "0x7552Ed65a45E27740a15B8D5415E90d8ca64C109"
 
+    def test_constructor(self):
+        ethereum_network = EthereumNetwork.RINKEBY
+        base_url = "https://safe.global"
+        transaction_service_api = TransactionServiceApi(
+            ethereum_network, ethereum_client=None, base_url=base_url
+        )
+        self.assertEqual(transaction_service_api.network, ethereum_network)
+        self.assertIsNone(transaction_service_api.ethereum_client)
+        self.assertEqual(transaction_service_api.base_url, base_url)
+
+    def test_from_ethereum_client(self):
+        with self.assertRaisesMessage(EthereumNetworkNotSupported, "GANACHE"):
+            TransactionServiceApi.from_ethereum_client(self.ethereum_client)
+
+        with mock.patch.object(
+            EthereumClient, "get_network", return_value=EthereumNetwork.RINKEBY
+        ):
+            transaction_service_api = TransactionServiceApi.from_ethereum_client(
+                self.ethereum_client
+            )
+            self.assertEqual(
+                transaction_service_api.ethereum_client, self.ethereum_client
+            )
+            self.assertEqual(transaction_service_api.network, EthereumNetwork.RINKEBY)
+
     def test_data_decoded_to_text(self):
         test_data = {
             "method": "multiSend",
@@ -58,7 +85,7 @@ def test_data_decoded_to_text(self):
                 }
             ],
         }
-        decoded_data_text = self.transaction_service.data_decoded_to_text(test_data)
+        decoded_data_text = self.transaction_service_api.data_decoded_to_text(test_data)
         self.assertIn(
             "- changeMasterCopy: 0x34CfAC646f301356fAa8B21e94227e3583Fe3F5F",
             decoded_data_text,
@@ -69,9 +96,9 @@ def test_data_decoded_to_text(self):
         )
 
     def test_get_balances(self):
-        balances = self.transaction_service.get_balances(self.safe_address)
+        balances = self.transaction_service_api.get_balances(self.safe_address)
         self.assertIsInstance(balances, list)
 
     def test_get_transactions(self):
-        transactions = self.transaction_service.get_transactions(self.safe_address)
+        transactions = self.transaction_service_api.get_transactions(self.safe_address)
         self.assertIsInstance(transactions, list)