I'm not sure what you're referring to, but SPC j n and pressing enter while on input mode add newlines on the repl buffer

C-RET in Evil insert state or Emacs to span your code over multiple lines in the Clojure REPL buffer. C-j and C-k cycle through the REPL history https://practicalli.github.io/spacemacs/evaluating-clojure/evaluate-in-repl-buffer.html

Its more common to write code in source code files and evaluate specific expressions as you write or change them. https://practicalli.github.io/spacemacs/evaluating-clojure/

also see the useful cider-scratch-buffer, if you want a place to evaluate forms without throwing them into tracked files

Thanks that’s helpful!