Access token - Invalid Checksum error

Hi - I've been using Kite Connect to connect to Zerodha. It's been working fine, but have recently started getting 'Invalid Checksum' error while trying to get access token. Please see below the code snippet I'm using. I had raised a support ticket on Zerodha but they replied with a generic response pointing me to API documentation and asked me to re-install PI (when I'm not at all using Pi in the first place)

Appreciate any help. Code snippet below. API KEY and SECRET KEY are as provided for my Zerodha app

try:
kite = KiteConnect(api_key = api_key)
print(kite.login_url())
except Exception as e:
print (e)

rt = request token copied from the URL after pasting the above login.URL

try:
user = kite.request_access_token(request_token = rt, secret=api_secret)
access_token = print(user["access_token"])
except Exception as e:
print (e)

Invalid checksum