Relocate api build output to a different location does not work as expected

[msedi]

Maybe a really stupid question. In our environment all our build output goes to a single _Build directory to have a single point to cleanup the project environment. Deleting the directory restores the project to zero.

Using docfx the default is that the api is built next to the docfx.json. To relocate the api into the _Build folder, I used:

 "metadata": [
    {
      "src": [
        {"src": "../Libraries/Dev", "files": ["**/*.csproj"]}
      ],
      "dest": "../_Build/docfx/api"
    }
  ],

and adapted the build to use the new folder

"build": {
    "content": [
      {"files": ["**/*.{md,yml}"]},
      {"files": ["**/*.{md,yml}"], "src": "../_Build/docfx/api/", "dest": "api/"}
    ],

This works fine, the api folder is relocated and the content is taken.
What does not work is that when it is relocated, the API cannot be reached anymore in toc.yml

- name: Introduction
  href: introduction.md
- name: Getting Started
  href: getting-started.md
- name: API
  href: api/

What I get when clicking on the API button to show the API, is simply a list of files, but API documentation page.
I assume its easy, but I didn't find how this should work.

Thanks for the help!