Problem with Ecto prefix: usage

I am attempting to use the prefix: attribute in my queries so that I can control which mySQL database I am reading/writing from.

When I attempt a Repo.get_by() call, Elixir moans that t.prefix doesn’t exist (or something similar to that) - Ecto thinks the prefix: attribute is a table field (column) and not the indication of which database to query.

Repo.get_by(Ticket, ticket: ticket_params[:ticket], prefix: "other_db")

The prefix: attribute seems(?) to work okay with other query types like Repo.insert!(prefix: "other_db") or Repo.get!(Ticket, id, prefix: "other_db") or Repo.all(prefix: "other_db"), etc.

What am I doing wrong?