为啥会报text read only

Emacs-general
1 
(defun my-vertico-posframe--prettify-buffer (&rest _)
  "Add top and bottom margin to the prompt."
  (with-current-buffer vertico-posframe--buffer
    (goto-char (point-min))
    (insert (propertize "\n" 'face '(:height 0.3) 'read-only t))
    (message "new line inserted")
    (goto-char (point-max))
    (insert (propertize "\n" 'face '(:height 0.3) 'read-only t)))
  )

(advice-add #'vertico-posframe--display :after #'my-vertico-posframe--prettify-buffer)

想仿照centaur emacs 给vertico-posframe 给posframe添加上下间距，但是一直报text read only.

2 
(let ((inhibit-read-only t))
  ...
  (insert "text")
  ...)