how can i pass branch name in webhook url?

Currently under the same gitlab, I configure webhook in repo A to trigger the pipeline of repo B, the url is similar to this: api/v4/projects/project/ref/dev/trigger/pipeline? variables[WEBHOOK_BRANCH]= ${CI_COMMIT_REF_NAME} , but I can't get the branch name of repo A in the pipeline of repo B, is there any other way?