Same problem here

Same here, with newer version too.
If we assign to grafana a root_url ending in /grafana, the plugin seems that doesn't do the resurrection, pointing to /api, instead of /grafana/api

Solved in 1.9.13
5f5eefb

Recently we made some changes to the way Grafana OnCall is initialized. Use 1.9.22, there were quite a few changes along the way from 1.9.0-1.9.22 to get things working.

• If you are running Grafana 11 and newer you must have externalServiceAccounts feature toggle enabled.
  This has already been enabled in the docker compose files and helm charts in the oncall repo.
• Plugin settings must be provided to the plugin using an API call if you are installing for the first time (Note: credentials and hostnames need to be adjusted for your configuration, stackId and orgId are expected to be the listed constants in a self-hosted configuration)

curl -X POST 'http://admin:admin@localhost:3000/api/plugins/grafana-oncall-app/settings' -H "Content-Type: application/json" -d '{"enabled":true, "jsonData":{"stackId":5, "orgId":100, "onCallApiUrl":"http://engine:8080/", "grafanaUrl":"http://grafana:3000/"}}'

• Once settings are configured use this API call to install:

curl -X POST 'http://admin:admin@localhost:3000/api/plugins/grafana-oncall-app/resources/plugin/install'

Grafana OnCall should now be ready to use.
For additional troubleshooting see here