Microsoft.Identity.Client.MsalServiceException

Question

I am trying to send emails from my angularjs application using MSAL setup, getting these exceptions:

Exception thrown: 'System.Net.WebException' in mscorlib.dll Exception thrown: 'Microsoft.Identity.Client.MsalServiceException' in Microsoft.Identity.Client.dll Exception thrown: 'Azure.Identity.AuthenticationFailedException' in Azure.Identity.dll

I am trying to send emails from my angularjs application using MSAL setup, got the access tokens with scopes including mail.send, then I am sending the accesstoken to ASP.NET to configure with graphclient using OnBehalfOfCredential. but getting exceptions.

msalServiceFactory.getEmailToken = function () {
    const account = msalInstance.getAllAccounts()[0]; 
    const emailScopes = ["Mail.Send"];
    const silentRequest = {
        scopes: emailScopes,
        account: account
    };
    return msalInstance.acquireTokenSilent(silentRequest).then(response => {
        console.log("Token acquired silently", response.accessToken);
        return response.accessToken;
    }).catch(error => {
        console.error("Silent token acquisition failed", error);
        if (error instanceof msal.InteractionRequiredAuthError) {
            return msalInstance.acquireTokenPopup({ scopes: emailScopes }).then(response => {
                console.log("Token acquired via popup", response.accessToken);
                return response.accessToken;
            }).catch(innerError => {
                console.error("Interactive token acquisition failed", innerError);
                return null;
            });
        } else {
            return null;
        }
    });
}

return msalServiceFactory;
    private  void GraphServiceClient(string accessToken)
    {
        try
        {
            var scopes = new[] { "https://graph.microsoft.com/.default" };

            // Multi-tenant apps can use "common",
            // single-tenant apps must use the tenant ID from the Azure portal
            var tenantId = _graphTenanatId;

            // Values from app registration
            var clientId = _graphClientId;
            var clientSecret = _graphClientSecret;

            // using Azure.Identity;
            var options = new OnBehalfOfCredentialOptions
            {
                AuthorityHost = AzureAuthorityHosts.AzurePublicCloud,
            };

            // This is the incoming token to exchange using on-behalf-of flow
            var oboToken = accessToken;

            var onBehalfOfCredential = new OnBehalfOfCredential(
                tenantId, clientId, clientSecret, oboToken, options);

            _graphServiceClient =  new GraphServiceClient(onBehalfOfCredential, scopes);
            if (_graphServiceClient == null)
            {
                throw new InvalidOperationException("Failed to initialize GraphServiceClient.");
            }
        }
        catch (MsalUiRequiredException msalEx)
        {
            LogRepository.LogMessage(this.GetType().FullName + ": MSAL UI required exception in InitGraphServiceClient: " + msalEx.ToString());
            throw;
        }
        catch (Exception ex)
        {
            LogRepository.LogMessage(this.GetType().FullName + ": An error occurred in InitGraphServiceClient: " + ex.ToString());
            throw;
        }
    } and sending email like this     // Send mail as the authenticated user
            await _graphServiceClient.Me.SendMail.PostAsync(sendMailBody);