Manage Secrets REST API - error 428 Precondition required

Question:
I am trying to use the Manage Secrets REST API, but it failed even if I followed all steps in doc. It fails with API Playgroup(Generated Token and Access Token), Postman(I can get access_token) and curl.

Product:
Wix Studio Free

What are you trying to achieve:
Use the Manage Secrets API to List/GET, Create/POST.

What have you already tried:

Additional information:
image