PayPal API – Authorization header does not have valid access token

July 12, 2024

I’m trying to use the PayPal API with this code to get a Valid Token:

var clientId = "yyyy";
var secret = "xxxx";

var client = new RestClient("https://api-m.sandbox.paypal.com/");
client.AddDefaultHeader("Authorization", "Basic " + 
Convert.ToBase64String(Encoding.UTF8.GetBytes(string.Format("{0}:{1}", clientId, 
secret))));
var request = new RestRequest("v1/oauth2/token", Method.Post);
request.AddParameter("grant_type", "client_credentials");
    
var response = await client.ExecuteGetAsync(request);

But the response coming back is:

{"error":"invalid_token","error_description":"Authorization header does not have valid access token"}

Is there something I’m missing, when I use Postman, I have the exact same parameters filled in Postman with my C# code as well.

>Solution :

Try switching the request class to a different one.
For example you could use HttpClient

    var clientId = "yyyy";
    var secret = "xxxx";

    using (var client = new HttpClient())
    {
        client.BaseAddress = new Uri("https://api-m.sandbox.paypal.com/");

        var authToken = Convert.ToBase64String(Encoding.UTF8.GetBytes($"{clientId}:{secret}"));
        client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Basic", authToken);

        var requestContent = new FormUrlEncodedContent(new[]
        {
            new KeyValuePair<string, string>("grant_type", "client_credentials")
        });

        var response = await client.PostAsync("v1/oauth2/token", requestContent);

        response.EnsureSuccessStatusCode();

        var responseBody = await response.Content.ReadAsStringAsync();
    }