Can't get blame from the gitlab api

It seems never works as the doc says bellow:

In my case,
The API URL is:/api/v4/projects/9/repository/files/config.json/blame?ref=master,
It always says “{“error”:“404 Not Found”}” when I try to get a blame of a file.
Anyone know why?

By the way it is ok to get raw file.
URL: /api/v4/projects/9/repository/files/config.json/raw?ref=master

I think there should be have somewhere to turn on this API,
Is there anyone know how?

still struggle on it.
Anyone can give some help?

I have the same problem.

After complex verification, I learned that this problem may be caused by the problem of gitlab version.
If your gitlab version supports V4 API, You can get the gitlab version through the GET method:

curl --location --request GET 'https://{GITLAB_URL}/api/v4/version' \

and then you can find your current version’s doc from url:

You need to switch tag to your gitlab version

Happy development!