Error on create adaccount for a child Business Manager with facebook's graph API

Question

At the moment I am trying to create a system where you can create several business managers, each one associated with its own Adaccount.

Documentation link: https://developers.facebook.com/docs/marketing-api/2tier-bm-solution/guides/setup-cbm

When I try to create an adaccount from a child business manager ID by following the creation process that is on the documentation, I get the following error:

"code": 400,
    "message": {
        "message": "Unsupported post request. Object with ID '123XXXXXX' does not exist, cannot be loaded due to missing permissions, or does not support this operation. Please read the Graph API documentation at https://developers.facebook.com/docs/graph-api",
        "type": "GraphMethodException",
        "code": 100,
        "error_subcode": 33,
        "fbtrace_id": "AbXl_ADPwTNTkFVtIJvozW5"
    }
}

I have already spent several days looking for a solution, but the documentation is not explicit enough about this and also the answer to the error is quite general. I would like you to help me to solve this please.

I put all the requested permissions in the documentation, but it keeps doing the same thing.