diff --git a/src/opengradient/client/opg_token.py b/src/opengradient/client/opg_token.py
index 864dd64..acf59c7 100644
--- a/src/opengradient/client/opg_token.py
+++ b/src/opengradient/client/opg_token.py
@@ -95,12 +95,26 @@ def _send_approve_tx(
         nonce = w3.eth.get_transaction_count(owner, "pending")
         estimated_gas = approve_fn.estimate_gas({"from": owner})
 
+        # Check native (ETH) balance to cover gas before building/sending tx.
+        gas_price = w3.eth.gas_price
+        gas_limit = int(estimated_gas * 1.2)
+        total_cost = gas_limit * gas_price
+        native_balance = w3.eth.get_balance(owner)
+        if native_balance < int (total_cost * 1.1):  # Add a 10% buffer to avoid underestimating
+            needed_eth = Web3.from_wei(total_cost, "ether")
+            have_eth = Web3.from_wei(native_balance, "ether")
+            raise RuntimeError(
+                f"Insufficient native balance for gas on {w3.eth.chain_id}. "
+                f"Required: {needed_eth:.6f} ETH, Available: {have_eth:.6f} ETH. "
+                f"Please fund your wallet at the Base Sepolia faucet."
+            )
+
         tx = approve_fn.build_transaction(
             {
                 "from": owner,
                 "nonce": nonce,
-                "gas": int(estimated_gas * 1.2),
-                "gasPrice": w3.eth.gas_price,
+                "gas": gas_limit,
+                "gasPrice": gas_price,
                 "chainId": w3.eth.chain_id,
             }
         )
diff --git a/tests/opg_token_test.py b/tests/opg_token_test.py
index b237ccd..abaa2db 100644
--- a/tests/opg_token_test.py
+++ b/tests/opg_token_test.py
@@ -50,12 +50,26 @@ def _setup_approval_mocks(mock_web3, mock_wallet, contract):
     approve_fn = MagicMock()
     contract.functions.approve.return_value = approve_fn
     approve_fn.estimate_gas.return_value = 50_000
-    approve_fn.build_transaction.return_value = {"mock": "tx"}
+    
+    # 1. Update build_transaction to include required fields for the signer
+    approve_fn.build_transaction.return_value = {
+        "gas": 50_000,
+        "gasPrice": 1_000_000_000,
+        "nonce": 7,
+        "chainId": 84532,
+        "to": SPENDER_ADDRESS,
+        "data": "0x",
+        "from": OWNER_ADDRESS
+    }
 
     mock_web3.eth.get_transaction_count.return_value = 7
     mock_web3.eth.gas_price = 1_000_000_000
     mock_web3.eth.chain_id = 84532
 
+    # 2. Add the ETH balance mock so your new pre-flight check passes
+    # We give it 10 ETH by default so existing tests don't "starve" for gas
+    mock_web3.eth.get_balance.return_value = 10 * 10**18 
+
     signed = MagicMock()
     signed.raw_transaction = b"\x00"
     mock_wallet.sign_transaction.return_value = signed
@@ -215,3 +229,4 @@ def test_large_amount(self, mock_wallet, mock_web3):
 
         assert result.allowance_before == expected_base
         assert result.tx_hash is None
+# --- Add this at the very end of opg_token_test.py ---
\ No newline at end of file