Hi @shinchan you are using the wrong image to connect with your backend. We have come a long way and there are many changes which could have played the role in error. Please use image dgraph/dgraph:v21.03-slash.
Sample script would be
#!/usr/bin/env bash
DEPLOYMENT_URL="your-backend-url"
DEPLOYMENT_JWT="<deployment-jwt>"
docker run -it --rm -v /users/dgraph/downloads:/tmp dgraph/dgraph:v21.03-slash \
dgraph live --slash_grpc_endpoint=${DEPLOYMENT_URL}:443 -f /tmp/1million.rdf.gz -t ${DEPLOYMENT_JWT}
Deployment JWT is the api key you can generate from the API Key tab on settings page. Do remember it takes about 30 sec for the api key to get active once generated.