fix fallback when trying insertion of already existing transaction

src/main.py

@@ -149,18 +149,13 @@ async def process_transaction(
     try:
         # Insert every single transaction into the database
         transaction = insert_transaction(db, transaction)
-    except UniqueViolation:
-        logger.warning("Transaction already exists in the database - retrieving it")
-        return get_fraud_status(
+    except (UniqueViolation, IntegrityError):
+        logger.warning("Transaction cannot be inserted in the database - checking existence...")
+        db.rollback()
+        return await get_fraud_status(
             transaction_number=transaction.transaction_number,
             db=db
         )
-    except IntegrityError as e:
-        logger.error(e)
-        raise HTTPException(
-            status_code=HTTP_422_UNPROCESSABLE_ENTITY,
-            detail=f"Transaction {transaction.transaction_number} is not valid. Check input values."
-        )
     except Exception as e:
         logger.error(e)
         raise HTTPException(