I am having trouble with the error shown in the image. Does anyone know how to solve this problem?
I would like to obtain a refresh token to use the "YouTube Data API v3".

I tried the following behavior.

1. Create a WEB type Client ID in the GCP console in advance.
2. Access https://developers.google.com/oauthplayground/, set the client ID and client secret in "1.", select https://www...../youtube and https://www...../youtube.upload from YouTube Data API v3, and then Authorize APIs execution.
3. When asked which account to use for OAuth
   If you select my brand account, Google will block it as shown in the image.

[What I tried to solve]

• The newly created Google account was able to obtain a token.
  → However, I really need to use the Youtube API with a branded account I already have.
• I have tried turning on "Less secure app access" in the security settings of my branded account, but this did not solve the problem.
• The target brand account is not managed by GoogleWorkspace.

Any information would be appreciated, I will provide any information needed, so if anyone knows anything, please help me.