@jcomplex: hey! I'd say schema is telling you that it found the keyword :id where it expected to find something sequential. For instance I got this in ly repl:

(require '[schema.core :as s])
=> nil
(s/check [s/Keyword]  [:id])
=> nil
(s/check [s/Keyword] :id)
=> (not (sequential? :id))
(s/check [s/Str] :id)
=> (not (sequential? :id))

In the second and third checks, schema expects a sequence of something and got something instead (in these cases the keyword :id)