Fetch ChannelId by username using Youtube V3 API

I am working on a project that requires that I get the channelId of a User using their username with the Youtube V3 API and I'm facing some difficulty understanding what to set as the value of the "forUsername" param.

Looking at it, I believe that my misunderstanding comes from using the Account handle as the Username since while the request below

https://www.googleapis.com/youtube/v3/channels?key=API_KEY&forUsername=ganba_roll&part=id

(Example for https://www.youtube.com/@ganba_roll)

doesn't return any results:

{"kind": "youtube#channelListResponse","etag": "RuuXzTIr0OoDqI4S0RU6n4FqKEM","pageInfo": {"totalResults": 0,"resultsPerPage": 5    }}

A similar question's answer that used the request below as an example of how to retrieve a users channelId with the v3 API

https://www.googleapis.com/youtube/v3/channels?key=API_KEY&forUsername=klauskkpm&part=id

successfully returns

{"kind": "youtube#channelListResponse","etag": "_eCbyZfbnzEHno7A-oBcP0LCzlI","pageInfo": {"totalResults": 1,"resultsPerPage": 5    },"items": [       {"kind": "youtube#channel","etag": "JhuO0pv2b8motmYfYWvQrmif2a8","id": "UCfjTOrCPnAblTngWAzpnlMA"       }    ]}

I'm confused as to where to retrieve the value that I need to set the forUsername param to.

Thank you for your time!