I am accessing API in dyanmics 365 BC using asp.net core 8 token issue

Question

I am accessing API in dyanmics 365 BC using asp.net core 8 token issue

BC Dev 0

When I am accessing the API in Dynamics 365 Business Central using ASP.NET Core 8, but I am facing a token issue

this is my code for token Generate

private async Task<string> GetAccessToken()

{

using var client = new HttpClient();

var url = "https://login.microsoftonline.com/7xxxxxx9/oauth2/v2.0/token";

var body = new Dictionary<string, string>

{

    { "grant_type", "client_credentials" },

    { "client_id", "a3xxxxxx5" },

    { "client_secret", "BFNxxxxxx~" }, // 🔒 move to config later

    { "scope", "https://api.businesscentral.dynamics.com/.default" }

};

var content = new FormUrlEncodedContent(body);

var response = await client.PostAsync(url, content);

var json = await response.Content.ReadAsStringAsync();

var tokenObj = JsonSerializer.Deserialize<TokenResponse>(json);

return tokenObj.access_token;
```}

public class TokenResponse

{

```sql
public string access_token { get; set; }
```}

Viorel 126.8K Reputation points

2026-03-31T09:36:43.2866667+00:00

Is there any error message with some details?

Sridevi Machavarapu 26,185 Microsoft External Staff Moderator

Hello BC Dev,

The error indicates the token request is not being accepted. Since it works in Postman, the setup is fine and the issue is with how the request is sent from your code.

Please check the client secret in Microsoft Entra ID and ensure you’re using the secret value, not the secret ID. If unsure, create a new secret and update it.

Also make sure your code aligns with Postman:

Same tenant ID
Same client ID and secret
Same endpoint type (v1 uses resource, v2 uses scope)

Here is a working example using v2:

using System.Text.Json;
private async Task<string> GetAccessToken()
{
    using var client = new HttpClient();
    var url = "https://login.microsoftonline.com/{tenant-id}/oauth2/v2.0/token";
    var body = new Dictionary<string, string>
    {
        { "grant_type", "client_credentials" },
        { "client_id", "<client-id>" },
        { "client_secret", "<client-secret>" },
        { "scope", "https://api.businesscentral.dynamics.com/.default" }
    };
    var response = await client.PostAsync(url, new FormUrlEncodedContent(body));
    var json = await response.Content.ReadAsStringAsync();
    if (!response.IsSuccessStatusCode)
        throw new Exception($"Token error: {json}");
    var token = JsonSerializer.Deserialize<TokenResponse>(json);
    return token?.access_token;
}
public class TokenResponse
{
    public string access_token { get; set; }
}

If your Postman setup uses v1:

var url = "https://login.microsoftonline.com/{tenant-id}/oauth2/token";
var body = new Dictionary<string, string>
{
    { "grant_type", "client_credentials" },
    { "client_id", "<client-id>" },
    { "client_secret", "<client-secret>" },
    { "resource", "https://api.businesscentral.dynamics.com" }
};

Also confirm the app is added in Dynamics 365 Business Central with the required permissions.

Reference:

https://learn.microsoft.com/en-us/dynamics365/business-central/dev-itpro/administration/automation-apis-using-s2s-authentication#set-up-service-to-service-authentication

BC Dev 0 Reputation points

2026-04-01T02:34:45.81+00:00

Error is

Status: Unauthorized {"error":{"code":"Authentication_InvalidCredentials","message":"The server has rejected the client credentials. CorrelationId: 42590f31-29f2-4ef4-9d87-cb7fbcbf02e7."}}

when I used postman created token, code is working fine
Sridevi Machavarapu 26,185 Reputation points Microsoft External Staff Moderator

2026-04-02T17:15:11.0733333+00:00

Hello BC Dev,

Could you include how you generated token via Postman, what authentication flow and parameters used? Please share screenshots here if possible.