curl "https://www.lcpdfr.com/applications/downloadsng/interface/api.php" \
  -H "User-Agent: CyanCallouts/1.0 (+https://www.lcpdfr.com/profile/9-cyan/)" \
  -d "do=checkForUpdates" \
  -d "fileId=7792" \
  -d "textOnly=1"

  public static string GetLatestVersion(int fileId)
  {
      string updateEndpoint = "http://www.lcpdfr.com/applications/downloadsng/interface/api.php?do=checkForUpdates&fileId={0}&textOnly=true";
      string latestVersion = null;
      try {
          using(WebClient client = new WebClient()) {
              client.Headers.Add("user-agent", "CyanCallouts/1.0 (+https://www.lcpdfr.com/profile/9-cyan/)");
              latestVersion = client.DownloadString(string.Format(updateEndpoint, fileId));
          }
      }
      catch(Exception e) {
              // Failed. Maybe log the exception.
      }
      return latestVersion;
  }

0.4.9 (Build 8678)

curl "https://www.lcpdfr.com/applications/downloadsng/interface/api.php" \
  -H "User-Agent: CyanCallouts/1.0 (+https://www.lcpdfr.com/profile/9-cyan/)" \
  -d "do=getAssemblies" \
  -d "fileId=7792" 

/*
 * This is an example of an async function that tries to retrieve the latest LSPDFR assembly version
 */
using System.Text.Json;
using System.Net;
using System;

public class AssemblyInfoRetriever
{
    private static readonly HttpClient client = new HttpClient();

    public static async Task<string> GetLSPDFRAssemblyVersionAsync()
    {
        string url = "https://www.lcpdfr.com/applications/downloadsng/interface/api.php?do=getAssemblies&fileId=7792";
        string assemblyVersion = null;

        try
        {
            var response = await client.GetStringAsync(url);
            using (JsonDocument doc = JsonDocument.Parse(response))
            {
                JsonElement root = doc.RootElement;
                string error = root.GetProperty("error").GetString();

                if (string.IsNullOrEmpty(error))
                {
                    foreach(JsonProperty file in root.GetProperty("result").GetProperty("files").EnumerateObject()) {
                        if (file.Value.TryGetProperty("plugins/LSPD First Response.dll", out JsonElement versionElement)) {
                            assemblyVersion = versionElement.GetString();
                        }
                    }
                }
            }
            if(assemblyVersion == null) {
                throw new Exception("Couldn't find LSPDFR dll within result!");
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine("Error occurred: " + ex.Message);
        }

        return assemblyVersion;
    }
}

{
  "error": "",
  "result": {
    "files": {
      "lspdfr_049_8678_setup.exe": {},
      "LSPDFR_049_8678_Manual_Install.zip": {
        "DdsConvert.dll": "1.0.0.0",
        "DiscordRpcNet.dll": "1.0.0.0",
        "EasyHook.dll": "2.7.6578.0",
        "EasyLoad64.dll": "2.7.6578.0",
        "Gwen.dll": "1.0.0.0",
        "Gwen.UnitTest.dll": "1.0.0.0",
        "LMS.Common.dll": "1.0.0.0",
        "LMS.PortableExecutable.dll": "1.0.0.0",
        "lspdfr\/LSPDFR Configurator.exe": "1.0.0.0",
        "lspdfr\/Microsoft.Expression.Drawing.dll": "4.5.0.0",
        "Microsoft.Expression.Drawing.dll": "4.5.0.0",
        "Microsoft.VisualStudio.QualityTools.UnitTestFramework.dll": "10.0.0.0",
        "Mono.Cecil.dll": "0.9.6.0",
        "Mono.Cecil.Mdb.dll": "0.9.6.0",
        "Mono.Cecil.Pdb.dll": "0.9.6.0",
        "Mono.Cecil.Rocks.dll": "0.9.6.0",
        "plugins\/LSPD First Response.dll": "0.4.8678.25591",
        "RAGEPluginHook.exe": "1.0.0.0",
        "SlimDX.dll": "4.0.13.43",
        "System.ValueTuple.dll": "4.0.2.0"
      }
    }
  }
}