Invalid API key or access key

Kite connect is active and can able to access historical data. But trade execution is giving error with" invalid appi key or access key."
Text files reading and writing keys correctly.

code:

logging.basicConfig(level=logging.DEBUG)
access = open(r"access_token.txt","r")
access_token=access.read()
access.close()
key = open(r"api_key.txt","r")
api_k=key.read()
key.close()

kite = KiteConnect(api_key=api_k)
kite.set_access_token(access_token)

try:
order = kite.place_order(exchange='NSE',
tradingsymbol='SBIN',
transaction_type="BUY",
quantity=1,
# price=price,
product='MIS',
order_type='MARKET',
validity='DAY',
# trigger_price='0',
# disclosed_quantity=None,
# squareoff=target,
# stoploss=stoploss_buy,
#trailing_stoploss=trailing_loss,
variety="Regular")
print(order)
except Exception as e:
print(e)