Unable to invite external users

Describe the bug

I am trying to invite external user to sharePoint library. Only able to add with exting users (external/organizational) with their respective emails. However when tried to add new external user it says

Working fine with invitation sent from Sharepoint Portal
There is no issue when tried from Developer Graph Explorer itself
Working code

Post: https://graph.microsoft.com/v1.0/drives/b!MWXmufRKuUOoXtfXl2mrn97AHlHIfilDiYetCGFDjblVW8RXsw5ET5IGpX8VxdeB/root/invite
Request Body: {
  "recipients": [
    {
      "email": "gopal@gmail.com"
    }
  ],
  "message": "You have been invited to access the file.",
  "requireSignIn": true,
  "sendInvitationMessage": true,
  "roles": [
    "write"
  ],
  "notifyRecipients": true
}

The issue is just on "SDK" and "REST API using Http Client"

Authentication used
Using Azure authentication with Application based permission using client secret

Graph Permission Set

All allowed for cross tenant settings

Expected behavior

External users must be able to invited from SDK and Rest API. SharePoint portal and Developer Graph Explorer is working fine

How to reproduce

Not working code Sample

      public string DefaultScope = "https://graph.microsoft.com/.default";
       private GraphServiceClient _GraphService;
       internal GraphServiceClient Service
       {
           get
           {
               try
               {
                   if (_GraphService == null)
                   {
                       var scopes = new[] { DefaultScope };
                       var options = new TokenCredentialOptions
                       {
                           AuthorityHost = AzureAuthorityHosts.AzurePublicCloud
                       };
                       var clientSecretCredential = new ClientSecretCredential(TenantId, ClientId, ClientSecret, options);
                       var graphClient = new GraphServiceClient(clientSecretCredential, scopes);
                       _GraphService = graphClient;
                   }
                   return _GraphService;
               }
               catch (Exception ex)
               {
                   throw;
               }
           }
       }
//this works fine if email is AD user(organizational or External User)
//But if Email is some other user beside users in AD throws exception as above
public void InviteUser() {
   var recipients = new List<DriveRecipient>() { new DriveRecipient() { Email = "gopal@gmail.com" } };
   var diveId="b!WRqc2bfDTE2DkegjDrjE2j1bRgSiiIZJilysXZ3qHVKAyMwfK-OwRJuWBnso0xyz";
   var result = await Service.Drives[spRequest.ItemId].Root.Invite(recipients, true, new List<string>{"read""}, true, null, false).Request().PostAsync();
}

Even tried with the Rest API

private async Task<string> GetAccessTokenAsync()
{
    try
    {
        var credential = new ClientSecretCredential(TenantId, ClientId, ClientSecret);
        var tokenRequestContext = new TokenRequestContext(new[] { DefaultScope });
        var token = await credential.GetTokenAsync(tokenRequestContext);
        return token.Token;
    }
    catch(Exception ex)
    {
        throw;
    }
}

//works fine for existing users of AD
public async Task SendInviteAsync(string driveId, string email)
{
    try
    {
        using (HttpClient client = new HttpClient())
        {
            var token = await GetAccessTokenAsync();
            client.DefaultRequestHeaders.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("Bearer", token);
            client.DefaultRequestHeaders.Accept.Add(new System.Net.Http.Headers.MediaTypeWithQualityHeaderValue("application/json"));

            var requestBody = new
            {
                recipients = new[]
                {
            new { email }
        },
                message = "You have been invited to access the file.",
                requireSignIn = true,
                sendInvitationMessage = true,
                roles = new[] { "write" },
                notifyRecipients = true
            };

            string jsonBody = Newtonsoft.Json.JsonConvert.SerializeObject(requestBody);
            HttpContent content = new StringContent(jsonBody, Encoding.UTF8, "application/json");

            string url = $"https://graph.microsoft.com/v1.0/drives/{driveId}/root/invite";

            HttpResponseMessage response = await client.PostAsync(url, content);
            string responseContent = await response.Content.ReadAsStringAsync();

            if (response.IsSuccessStatusCode)
            {
                Console.WriteLine("✅ Invitation sent successfully!");
                Console.WriteLine(responseContent);
            }
            else
            {
                Console.WriteLine($"❌ Error: {response.StatusCode}");
                Console.WriteLine(responseContent);
            }
        }
    }
    catch(Exception ex)
    {

    }
}

SDK Version

Latest

Latest version known to work for scenario above?

No response

Known Workarounds

No response

Debug output

Code: sharingFailed
Message: Please configure B2B collaboration settings correctly and troubleshoot first, "https://aka.ms/b2b-troubleshoot". Error from Entra B2B: At least one invitation failed. Error: RequestCreationFailure, message: Failed to create invitation request.
Inner error:
AdditionalData:
date: 2025-03-19T10:44:37
request-id: 16fc6f7d-bae5-4225-a6d7-dbd8f5c13ac8
client-request-id: 16fc6f7d-bae5-4225-a6d7-dbd8f5c13ac8
ClientRequestId: 16fc6f7d-bae5-4225-a6d7-dbd8f5c13ac8

Configuration

No response

Other information

No response

Start with GraphServiceClient's Drives[...].Root.Invite call and the POST to /drives/{driveId}/root/invite, comparing both with the working Graph Explorer request. Inspect the sharingFailed response and its Entra B2B RequestCreationFailure details, then reproduce an invitation for a non-directory external email and confirm the SDK and REST paths behave consistently.