Promtail: “error sending batch, will retry” status=-1 context deadline exceeded”

[forums123]

I have a promtail client sending logs to a remote server.
My promtail config

server:
  http_listen_port: 9080
  grpc_listen_port: 0

positions:
  filename: /tmp/positions.yaml

clients:
  - url: http://<remote server>:3100/loki/api/v1/push

scrape_configs:
- job_name: system
  static_configs:
  - targets:
      - localhost
    labels:
      job: varlogs
      instance: <local server>
      __path__: /var/log/*.log

when I have my iptables configured like

Chain INPUT (policy DROP)
Chain OUTPUT (policy ACCEPT)

I get the error

msg="error sending batch, will retry" status=-1 tenant= error="Post \"http://<remote server>:3100/loki/api/v1/push\": context deadline exceeded"

When I change it to

Chain INPUT (policy ACCEPT)

it works.

Which ports needs to be configured in iptables. It seems that allowing outgoing traffic is not enough.
Thanks in advance!!

[forums123]

Anyone can help with configuring IP tables correctly?
Many thanks!!