JWT Token Failure

creating a private app that has no user interface, only server to Ring Central interface.

I tried this code snippet with the JWT Token created in my Sandbox with clientid and client-secret. I get the following error:

Unable to authenticate to platform. Check credentials.Either code, or username with password, or jwt has to be provided

CODE testest in python:

from ringcentral import SDK
import os,sys

rcsdk = SDK( os.environ.get('RC_CLIENT_ID'),
os.environ.get('RC_CLIENT_SECRET'),
os.environ.get('RC_SERVER_URL') )
platform = rcsdk.platform()

try:
    platform.login( jwt=os.environ.get('RC_JWT') )
except Exception as e:
    print(e)
    sys.exit("Unable to authenticate to platform. Check credentials." + str(e))

print(f'Login with JWT successful.')

My app works fine with a user login and password, which is not practical for distribution or as secure as a JWT.