Branches with slashes in their name (eg bugfix/issue-123, feature/abc) are not supported at the moment.
As a work around, replace the slash of the branch name in the URL with %2F, for example the bugfix/issue-123 branch URL https://github.com/your-org/yor-repo/blob/bugfix/issue-123/markdown/test-basic.md to https://github.com/your-org/yor-repo/blob/bugfix%2Fissue-123/markdown/test-basic.md
Let us know your use case here if you require support for slashes in branch names.