let*: Symbol’s function definition is void: \(setf\ elfeed-meta\)

[konstare]

Hello,

I am trying to write a function, which renames some feeds. I stumble upon the following problem, when i run the following function:

(defun my/elfeed-update-db2 ()
    (interactive)
  (elfeed-db-ensure)
    (let ((F  (elfeed-db-get-feed "https://nullprogram.com/feed/")))
      (setf (elfeed-meta F :title)  "AAA")))

i run this function in elfeed-search mode and get in the Message buffer:

let*: Symbol’s function definition is void: \(setf\ elfeed-meta\)

At the same time i can, without any error, run the following code:

(let ((F  (elfeed-db-get-feed "https://nullprogram.com/feed/")))
      (setf (elfeed-meta F :title)  "AAA"))

What is my mistake?
What is even the difference between trying to rename a feed in a function and without it?
Could you help me to figure it out?