Getting ArgumentOutOfRangeException error Idenity Server4 - identityserver4

Question

We are using Entity framework core with Identity server4 and getting the ArgumentOutOfRangeException when calling the token endpoint via code. Here is our ConfigurationServices method in Identity server project:
public void ConfigureServices(IServiceCollection services)
{
services.AddSingleton<IConfiguration>(Configuration);
string connectionString = Configuration.GetConnectionString("IdentityServer");
var rsaProvider = new RSACryptoServiceProvider(512);
SecurityKey key = new RsaSecurityKey(rsaProvider);
var credentials = new Microsoft.IdentityModel.Tokens.SigningCredentials
(key, SecurityAlgorithms.RsaSha512Signature);
var migrationsAssembly = typeof(Startup).GetTypeInfo().Assembly.GetName().Name;
services.AddIdentityServer()
.AddSigningCredential(credentials)
// this adds the config data from DB (clients, resources)
.AddConfigurationStore(options =>
{
options.ConfigureDbContext = builder =>
builder.UseSqlServer(connectionString,
sql => sql.MigrationsAssembly(migrationsAssembly));
}) // this adds the operational data from DB (codes, tokens, consents)
.AddOperationalStore(options =>
{
options.ConfigureDbContext = builder =>
builder.UseSqlServer(connectionString,
sql => sql.MigrationsAssembly(migrationsAssembly));
// this enables automatic token cleanup. this is optional.
// options.EnableTokenCleanup = true;
// options.TokenCleanupInterval = 30;
});
// Add S3 to the ASP.NET Core dependency injection framework.
services.AddAWSService<Amazon.S3.IAmazonS3>();
}
Here is our client application that calling identity server project("http://localhost:3000/"):
[HttpGet]
[AllowAnonymous]
public async Task<IActionResult> Get(string client, string secret)
{
IActionResult result = null;
//discover endpoints from metadata
var disco = await DiscoveryClient.GetAsync("http://localhost:3000/");
if (disco.IsError)
{
result = NotFound(disco.Error);
return result;
}
//request token
var tokenClient = new TokenClient(disco.TokenEndpoint, client, secret);
var tokenResponse = await tokenClient.RequestClientCredentialsAsync(scope: "sup");
if (tokenResponse.IsError)
{
result = NotFound(tokenResponse.Error);
}
result = Ok(tokenResponse.Json);
return result;
}
Here is error we have got: