I don’t know anything in particular about your course’s assignment, so I don’t know how much help I can be here.
That error message is indicating that the index name is not present in the file
.../config.toml (did you mean
../config.toml?). It would help to see the configuration file you’re trying to use.
I wonder if your configuration file is not updated for the changes in v2.3.0? In particular, as of v2.3.0 lines like
inverted-index = "some-path"
forward-index = "some-other-path"
were unified into one line like
index = "index-path"
and the forward and inverted indexes are placed as subdirectories within that path.