OnCall mobile app can't scan QR-code

Hello everyone.
I installed grafana and oncall via docker compose on a vps in a private network. Oncall API URL looks like http://oncall:8888 (it is not visible from the internet). Connected in Grafana to oncall backend, alerting works.
Next I made a grafana cloud account, added the oncall API URL to docker-compose.yml (GRAFANA_CLOUD_ONCALL_API_URL: https://oncall-prod-eu-west-0.grafana.net/oncall)
Added a token in the cloud version, connected using this token in the OSS version. The OSS show me a QR code. And I can’t scan this code with 3 phones. No any errors. Nothing is happened.

Has anyone ever had this? Can I use mobile app by another way?

Should the OSS OnCall backend be visible from the outside? I don’t have it visible and grafana worked fine…

Thank you.