diff --git a/frontend/src/components/TransactionsList.tsx b/frontend/src/components/TransactionsList.tsx
index a210116..3adb3a8 100644
--- a/frontend/src/components/TransactionsList.tsx
+++ b/frontend/src/components/TransactionsList.tsx
@@ -267,10 +267,7 @@ export default function TransactionsList() {
 
             return (
               <div
-                key={
-                  transaction.internal_transaction_id ||
-                   `${transaction.account_id}-${transaction.transaction_date}-${transaction.transaction_value}`
-                }
+                 key={`${transaction.account_id}-${transaction.transaction_id}`}
                 className="p-6 hover:bg-gray-50 transition-colors"
               >
                 <div className="flex items-start justify-between">
@@ -365,7 +362,7 @@ export default function TransactionsList() {
         isOpen={showRawModal}
         onClose={handleCloseModal}
         rawTransaction={selectedTransaction?.raw_transaction}
-        transactionId={selectedTransaction?.internal_transaction_id || "unknown"}
+        transactionId={selectedTransaction?.transaction_id || "unknown"}
       />
     </div>
   );
diff --git a/frontend/src/types/api.ts b/frontend/src/types/api.ts
index de7db2c..4e9f230 100644
--- a/frontend/src/types/api.ts
+++ b/frontend/src/types/api.ts
@@ -56,7 +56,8 @@ export interface RawTransactionData {
 }
 
 export interface Transaction {
-  internal_transaction_id: string | null;
+  transaction_id: string;  // NEW: stable bank-provided transaction ID
+  internal_transaction_id: string | null;  // OLD: unstable GoCardless ID
   account_id: string;
   transaction_value: number;
   transaction_currency: string;
diff --git a/leggend/api/models/accounts.py b/leggend/api/models/accounts.py
index 9588956..39c5e2c 100644
--- a/leggend/api/models/accounts.py
+++ b/leggend/api/models/accounts.py
@@ -36,7 +36,8 @@ class AccountDetails(BaseModel):
 class Transaction(BaseModel):
     """Transaction model"""
 
-    internal_transaction_id: Optional[str] = None
+    transaction_id: str  # NEW: stable bank-provided transaction ID
+    internal_transaction_id: Optional[str] = None  # OLD: unstable GoCardless ID
     institution_id: str
     iban: Optional[str] = None
     account_id: str
@@ -54,6 +55,7 @@ class Transaction(BaseModel):
 class TransactionSummary(BaseModel):
     """Transaction summary for lists"""
 
+    transaction_id: str  # NEW: stable bank-provided transaction ID
     internal_transaction_id: Optional[str] = None
     date: datetime
     description: str
diff --git a/leggend/api/routes/accounts.py b/leggend/api/routes/accounts.py
index e6f4362..63e9af2 100644
--- a/leggend/api/routes/accounts.py
+++ b/leggend/api/routes/accounts.py
@@ -243,7 +243,8 @@ async def get_account_transactions(
             # Return simplified transaction summaries
             data = [
                 TransactionSummary(
-                    internal_transaction_id=txn["internalTransactionId"],
+                    transaction_id=txn["transactionId"],  # NEW: stable bank-provided ID
+                    internal_transaction_id=txn.get("internalTransactionId"),
                     date=txn["transactionDate"],
                     description=txn["description"],
                     amount=txn["transactionValue"],
@@ -257,7 +258,8 @@ async def get_account_transactions(
             # Return full transaction details
             data = [
                 Transaction(
-                    internal_transaction_id=txn["internalTransactionId"],
+                    transaction_id=txn["transactionId"],  # NEW: stable bank-provided ID
+                    internal_transaction_id=txn.get("internalTransactionId"),
                     institution_id=txn["institutionId"],
                     iban=txn["iban"],
                     account_id=txn["accountId"],
diff --git a/leggend/api/routes/transactions.py b/leggend/api/routes/transactions.py
index 701bf3b..3f91d2e 100644
--- a/leggend/api/routes/transactions.py
+++ b/leggend/api/routes/transactions.py
@@ -75,7 +75,8 @@ async def get_all_transactions(
             # Return simplified transaction summaries
             data = [
                 TransactionSummary(
-                    internal_transaction_id=txn["internalTransactionId"],
+                    transaction_id=txn["transactionId"],  # NEW: stable bank-provided ID
+                    internal_transaction_id=txn.get("internalTransactionId"),
                     date=txn["transactionDate"],
                     description=txn["description"],
                     amount=txn["transactionValue"],
@@ -89,7 +90,8 @@ async def get_all_transactions(
             # Return full transaction details
             data = [
                 Transaction(
-                    internal_transaction_id=txn["internalTransactionId"],
+                    transaction_id=txn["transactionId"],  # NEW: stable bank-provided ID
+                    internal_transaction_id=txn.get("internalTransactionId"),
                     institution_id=txn["institutionId"],
                     iban=txn["iban"],
                     account_id=txn["accountId"],
diff --git a/tests/unit/test_api_transactions.py b/tests/unit/test_api_transactions.py
index bb99740..dc3cf61 100644
--- a/tests/unit/test_api_transactions.py
+++ b/tests/unit/test_api_transactions.py
@@ -15,6 +15,7 @@ class TestTransactionsAPI:
         """Test successful retrieval of all transactions from database."""
         mock_transactions = [
             {
+                "transactionId": "bank-txn-001",  # NEW: stable bank-provided ID
                 "internalTransactionId": "txn-001",
                 "institutionId": "REVOLUT_REVOLT21",
                 "iban": "LT313250081177977789",
@@ -24,9 +25,10 @@ class TestTransactionsAPI:
                 "transactionCurrency": "EUR",
                 "transactionStatus": "booked",
                 "accountId": "test-account-123",
-                "rawTransaction": {"some": "data"},
+                "rawTransaction": {"transactionId": "bank-txn-001", "some": "data"},
             },
             {
+                "transactionId": "bank-txn-002",  # NEW: stable bank-provided ID
                 "internalTransactionId": "txn-002",
                 "institutionId": "REVOLUT_REVOLT21",
                 "iban": "LT313250081177977789",
@@ -36,7 +38,7 @@ class TestTransactionsAPI:
                 "transactionCurrency": "EUR",
                 "transactionStatus": "booked",
                 "accountId": "test-account-123",
-                "rawTransaction": {"other": "data"},
+                "rawTransaction": {"transactionId": "bank-txn-002", "other": "data"},
             },
         ]
 
@@ -73,6 +75,7 @@ class TestTransactionsAPI:
         """Test retrieval of full transaction details from database."""
         mock_transactions = [
             {
+                "transactionId": "bank-txn-001",  # NEW: stable bank-provided ID
                 "internalTransactionId": "txn-001",
                 "institutionId": "REVOLUT_REVOLT21",
                 "iban": "LT313250081177977789",
@@ -82,7 +85,7 @@ class TestTransactionsAPI:
                 "transactionCurrency": "EUR",
                 "transactionStatus": "booked",
                 "accountId": "test-account-123",
-                "rawTransaction": {"some": "raw_data"},
+                "rawTransaction": {"transactionId": "bank-txn-001", "some": "raw_data"},
             }
         ]
 
@@ -105,6 +108,7 @@ class TestTransactionsAPI:
         assert len(data["data"]) == 1
 
         transaction = data["data"][0]
+        assert transaction["transaction_id"] == "bank-txn-001"  # NEW: check stable ID
         assert transaction["internal_transaction_id"] == "txn-001"
         assert transaction["institution_id"] == "REVOLUT_REVOLT21"
         assert transaction["iban"] == "LT313250081177977789"
@@ -116,6 +120,7 @@ class TestTransactionsAPI:
         """Test getting transactions with various filters."""
         mock_transactions = [
             {
+                "transactionId": "bank-txn-001",  # NEW: stable bank-provided ID
                 "internalTransactionId": "txn-001",
                 "institutionId": "REVOLUT_REVOLT21",
                 "iban": "LT313250081177977789",
@@ -125,7 +130,7 @@ class TestTransactionsAPI:
                 "transactionCurrency": "EUR",
                 "transactionStatus": "booked",
                 "accountId": "test-account-123",
-                "rawTransaction": {"some": "data"},
+                "rawTransaction": {"transactionId": "bank-txn-001", "some": "data"},
             }
         ]