Somehow I thought it worked automatically, but we had to provide the token. The configuration is based on Coveralls instructions to run parallel builds [1]. Alternatively we could use the Coveralls GitHub Action [2] which slightly simplifies the workflow configuration and removes the dependency of the coveralls gem. However, it also adds a dependency on simplecov-lcov and requires configuring it to renerate LCOV files on each run, so the benefits of using it are not that big. [1] https://docs.coveralls.io/parallel-build-webhook [2] https://github.com/coverallsapp/github-action/