Zoho Invoice API Error {"error":"invalid_client"} while requesting for token - zoho

Question

While accessing Zoho api to get the token I'm getting the following error:
{"error":"invalid_client"}
Step 1: I'm requesting for Auth Code and the auth code is returned successfully.
This is the API I'm using.
https://accounts.zoho.com/oauth/v2/auth?scope=xxx&client_id=yyyyy&state=zzzz&response_type=code&redirect_uri=pppppp&access_type=offline
Step 2: Token Request
With the Auth Code obtained in Step-1 I'm doing a post request for the token at that time only I'm getting the below exception.
var authTokenRequestData = new
{
code= code,
client_id= _clientId,
client_secret =_clientSecret,
redirect_uri = _redirectUri,
grant_type = "authorization_code"
};
var data = new StringContent(JsonConvert.SerializeObject(authTokenRequestData), Encoding.UTF8, "application/json");
var url = "https://accounts.zoho.com/oauth/v2/token";
string result = "";
using (var client = new HttpClient())
{
var response = await client.PostAsync(url, data);
result = await response.Content.ReadAsStringAsync();
}
It's giving me the exception
{error:invalid_client}
I've verified my client_id and client_secret. It's correct only.
It's Server-Based-Application client I've registered.
Any help is highly appreciated on this.

Answer 1

There could be one more reason for this issue.
{"error":"invalid_client"}
Check if you're using the correct domain. (.in .com or...)
For example, you're using .in instead of .com or vice-versa
In my case when I was using .in domain but my domain was .com I was getting the same error {"error":"invalid_client"}
I was using this:
var url = "https://accounts.zoho.in/oauth/v2/token";
I replaced it as below and that solved my issue.
var url = "https://accounts.zoho.com/oauth/v2/token";

Answer 2

I could solve this issue by changing the request Content-Type
"Content-Type", "application/x-www-form-urlencoded"
Complete code is as follows:
string _domain = ".in"; /*Ensure you're using the correct .com or .in domain*/
var url = "https://accounts.zoho"+ _domain + "/oauth/v2/token";
string result = "";
using (var client = new HttpClient())
{
var data = new Dictionary<string, string>
{
{ "Content-Type", "application/x-www-form-urlencoded" },
{ "code", code },
{ "client_id", _clientId },
{ "client_secret", _clientSecret },
{ "redirect_uri", _redirectUri },
{ "grant_type", "authorization_code" },
{ "access_type", "offline" }
};
var response = await client.PostAsync(url, new FormUrlEncodedContent(data));
result = await response.Content.ReadAsStringAsync();
}