Hi @tss.
Can you please verify whether you have whitelisted the IP from which you are making add index call.
Sample alpha command would be dgraph alpha --my=alpha:7080 --lru_mb=2048 --zero=zero:5080 --whitelist 0.0.0.0/0. I request you to go through this documentation.
If the issue still persists, please help us with logs/steps to debug?