How to get metrics from the channels I manage?

I'm trying to use the YouTube Analytics API to build a dashboard with the statistics of all my YouTube channels. The problem is that the API is not allowing me to get metrics from channels I'm managing.

The first problem is that I can't find any way to list all of the YouTube channels I manage. I'm using the following endpoint:

GET https://www.googleapis.com/youtube/v3/channels?part=snippet&mine=true

The thing is that I'm just getting the channels where I'm the owner. How can I get the ones I'm also managing?

Additionally, to get insights about those channels I'm using the following URL:

GET https://youtubeanalytics.googleapis.com/v2/reports?endDate={date}&startDate={date}&metrics={metrics}&ids=channel=={channel ID}

This works fine for the channels I own, but I get the following error for channels where I'm a manager:

{"error":{"code":403,"message":"Forbidden","errors":[{"message":"Forbidden","domain":"global","reason":"forbidden"}]}}

Any tips to make this work?