google admob api to create adUnit 403 - Stack Overflow

I used Go to call the Google AdMob API to create an ad unit, but it prompted me with a 403 error. I was calling the Google AdMob beta API. I could query the ad units correctly, but when creating, it indicated restricted permissions. I confirmed that I had used the correct permission scope. When I looked at the API documentation, it told me that "This method has limited access. If you see a 403 permission denied error, please reach out to your account manager for access."，In fact, the document does not provide the contact information of the relevant account manager.then I haven't found the contact information of the account manager，So, how should I call this creation method?

this is my test code:

var (
    clientID     = "my-client-id"
    clientSecret = "my-client-secret"
    redirectURL  = "my-redirect-url"
        scopes       = []string{admob.AdmobReadonlyScope, admob.AdmobReportScope,".monetization"}
)

func main() {
    ctx := context.Background()

    
    config := &oauth2.Config{
       ClientID:     clientID,
       ClientSecret: clientSecret,
       RedirectURL:  redirectURL,
       Scopes:       scopes,
       Endpoint:     google.Endpoint,
    }

    refreshToken := "my-refresh-token"
   
    tokenSource := config.TokenSource(ctx, &oauth2.Token{RefreshToken: refreshToken})

   
    newToken, err := tokenSource.Token()
    if err != nil {
       fmt.Printf("error:%s", err)
    }

    
    token := &oauth2.Token{
       AccessToken:  newToken.AccessToken,
       RefreshToken: refreshToken,
       TokenType:    "Bearer",
       Expiry:       time.Now().Add(1 * time.Hour),
    }

    
    client := config.Client(ctx, token)
    create(client)
}

func create(client *http.Client) {
    ctx := context.Background()
    admobService, err := admob.NewService(ctx, option.WithHTTPClient(client))
    if err != nil {
       panic(err)
    }

   
    adUnit := &admob.AdUnit{
       Name:        "pub-4926433235811020/adUnits/aabbccdd",
       DisplayName: "test_create_adunit",
       AdFormat:    "APP_OPEN",
       AdUnitId:    "aabbccdd",
       AppId:       "ca-app-pub-2783529062101020~1234567890",
       AdTypes:     []string{"RICH_MEDIA"},
    }
    result, err := admobService.Accounts.AdUnits.Create("accounts/my-account", adUnit).Do()
    if err != nil {
       fmt.Println(err)
    }
    fmt.Println(result)
}

Then the code execution result prompts: googleapi: Error 403: The caller does not have permission, forbidden.