Use the .NET SDK

dotnet add package Leadping.OpenApiClient
dotnet add package Microsoft.Kiota.Http.HttpClientLibrary

using Leadping.OpenApiClient;
using Microsoft.Kiota.Abstractions.Authentication;
using Microsoft.Kiota.Http.HttpClientLibrary;

var credential = Environment.GetEnvironmentVariable("LEADPING_API_KEY")
    ?? throw new InvalidOperationException("LEADPING_API_KEY is not set.");

var authProvider = new ApiKeyAuthenticationProvider(
    $"Bearer {credential}",
    "Authorization",
    ApiKeyAuthenticationProvider.KeyLocation.Header,
    ["api.leadping.ai"]);
var client = new LeadpingOpenApiClient(new HttpClientRequestAdapter(authProvider));
using var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(30));
var lead = await client.Leads["lead-id"].GetAsync(cancellationToken: timeout.Token)
    ?? throw new InvalidOperationException("Leadping returned no lead.");
Console.WriteLine(lead.Id);

var source = await client.Sources["source-id"].GetAsync();