Access to XMLHttpRequest at '' from origin '' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested

I have developed Asp.Net Core 3.1 API and deployed on the server through IIS, it’s working as expected if I send the GET/POST request from Postman or browser, But Below code is giving error.

$.ajax({
   type: 'GET',
   crossDomain: true,
   dataType: 'json',
   url: 'myUrl',
   success: function(jsondata){
   }
})

Error:

Access to XMLHttpRequest at
‘http://server:8080/API/GetMethod?currency=INR’
from origin ‘http://localhost:63765’ has been blocked by CORS policy:
No ‘Access-Control-Allow-Origin’ header is present on the requested
resource.

I have disabled the CORS from my application using the below code
C# code:

[DisableCors]
[Route("[controller]")]
[ApiController]
[AllowAnonymous]
public class APIController : ControllerBase
{

startup.cs

public void Configure(IApplicationBuilder app, IWebHostEnvironment env, ILoggerFactory loggerFactory)
{
loggerFactory.AddLog4Net();

if (env.IsDevelopment())
{
    app.UseDeveloperExceptionPage();
}

        

app.UseHttpsRedirection();

app.UseRouting();

app.UseCors();

app.UseAuthorization();

So I have tried disabling the CORS on controller level, I have tried jsonp also instead of JSON, It’s still getting the same error.

I have two questions here.

1. Is this clientside or serverside issue?
2. How to fix the error?

Note: I able to send GET requests from browser and Postman, but with this clientside code, I am getting the CORS related issue.

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddCors(options =>
        {
            options.AddPolicy(MyAllowSpecificOrigins,
                                builder =>
                                {
                                    builder.WithOrigins("http://example.com",
                                                        "http://www.contoso.com")
                                                        .AllowAnyHeader()
                                                        .AllowAnyMethod();
                                });
        });

        services.AddControllers();
    }