youtube data API v3 returns empty activity items

request url: https://www.googleapis.com/youtube/v3/activities?mine=true

• I used postman for this and made a request to youtube data api v3 using the url above. It returns an empty list in case of my "brand" account/channel. I use the brand account as my primary channel and it has all my activities

{"kind": "youtube#activityListResponse","etag": "jlYFzWSxnmZ8YXzm6DdHllY8jps","items": [],"nextPageToken": "CAUQAA","pageInfo": {"totalResults": 20,"resultsPerPage": 5    }}

however it works perfectly in case of my normal channel (set as the owner of the brand account/channel by default)

I have tried a few things:

• checked the permission on my brand channel: I am the owner
• checked if the app had access: it does have the relevant access

Does youtube data API v3 not support a brand account/channel?