Can't verify know on tangled.sh/knots #4

I've set up a knot using this docker compose:

services:
    knot:
        image: hqnna/knot:v1.6.0-alpha
        environment:
            KNOT_SERVER_HOSTNAME: ${KNOT_SERVER_HOSTNAME}
            KNOT_SERVER_OWNER: ${KNOT_SERVER_OWNER}
            KNOT_SERVER_SECRET: ${KNOT_SERVER_SECRET}
            KNOT_SERVER_DB_PATH: /app/knotserver.db
            KNOT_REPO_SCAN_PATH: /home/git/repositories
            KNOT_SERVER_INTERNAL_LISTEN_ADDR: localhost:5444
            APPVIEW_ENDPOINT: https://tangled.sh
        volumes:
            - ./keys:/etc/ssh/keys
            - ./repositories:/home/git/repositories
            - ./server:/app
        ports:
            - "5555:5555"
            - "2222:22"
        restart: on-failure

(The reverse-proxy is managed externally, I can access it from the browser)

But when adding it to tangled.sh, I'm getting "Failed to verify knot, unable to fetch owner."

I'm not familiar with architecture of tangled so I don't know what steps to take for debugging. I don't see any suspicious logs from the container:

finxol@akhaten:/srv/http/knot$ docker compose logs
knot-1  | s6-rc: info: service s6rc-oneshot-runner: starting
knot-1  | s6-rc: info: service s6rc-oneshot-runner successfully started
knot-1  | s6-rc: info: service fix-attrs: starting
knot-1  | s6-rc: info: service create-sshd-host-keys: starting
knot-1  | s6-rc: info: service fix-attrs successfully started
knot-1  | s6-rc: info: service legacy-cont-init: starting
knot-1  | s6-rc: info: service create-sshd-host-keys successfully started
knot-1  | s6-rc: info: service legacy-cont-init successfully started
knot-1  | s6-rc: info: service sshd: starting
knot-1  | s6-rc: info: service knotserver: starting
knot-1  | s6-rc: info: service sshd successfully started
knot-1  | s6-rc: info: service knotserver successfully started
knot-1  | s6-rc: info: service legacy-services: starting
knot-1  | s6-rc: info: service legacy-services successfully started
knot-1  | Server listening on 0.0.0.0 port 22.
knot-1  | Server listening on :: port 22.
knot-1  | time=2025-08-30T22:04:00.113Z level=INFO msg="successfully finished setting up hooks" command=knot
knot-1  | time=2025-08-30T22:04:00.117Z level=INFO msg="starting internal server" command=knot address=localhost:5444
knot-1  | time=2025-08-30T22:04:00.117Z level=INFO msg="starting main server" command=knot address=0.0.0.0:5555