I have integrated a Next.js (v14) frontend with an ASP.NET Core 8 Web API backend. I integration seems working However, when I comment out when I run the server the get API on Swagger gives the Status code 404 response.
I tried everything but things aren’t working.

using Microsoft.AspNetCore.SpaServices.AngularCli;
using System.Diagnostics;

namespace Next_API
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var builder = WebApplication.CreateBuilder(args);

            // Add services to the container.

            builder.Services.AddControllers();

            builder.Services.AddSpaStaticFiles(configuration =>
            {
                configuration.RootPath = "ClientApp/.next";
            });
            // Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle
            builder.Services.AddEndpointsApiExplorer();
            builder.Services.AddSwaggerGen();

            var app = builder.Build();

            if (app.Environment.IsDevelopment())
            {
                app.UseSwagger();
                app.UseSwaggerUI();
                app.UseDeveloperExceptionPage();

                var processStartInfo = new ProcessStartInfo
                {
                    FileName = "cmd.exe",
                    Arguments = "/c npm run dev", 
                    WorkingDirectory = Path.Combine(Directory.GetCurrentDirectory(), "ClientApp"),
                    RedirectStandardOutput = true,
                    RedirectStandardError = true,
                    UseShellExecute = false,
                    CreateNoWindow = true
                };

                var process = Process.Start(processStartInfo);
                process.OutputDataReceived += (sender, args) => Console.WriteLine(args.Data);
                process.ErrorDataReceived += (sender, args) => Console.WriteLine(args.Data);
                process.BeginOutputReadLine();
                process.BeginErrorReadLine();

                app.UseSpa(spa =>
                {
                    spa.UseProxyToSpaDevelopmentServer("http://localhost:3000");
                });
            }
            else
            {
                app.UseExceptionHandler("/Error");
                app.UseHsts();

                app.UseStaticFiles();
                app.UseSpaStaticFiles();

                app.UseSpa(spa =>
                {
                    spa.Options.SourcePath = "ClientApp";
                });
            }

            app.UseRouting();

            app.MapControllers();

            app.Run();
        }
    }
}

The API is not working status code 404 is the response everytime