public void ConfigureServices(IServiceCollection services)
{
	...
	services.AddSingleton<System.Net.Http.HttpClient>();
}

[Route("api/[controller]")]
[ApiController]
public class PingPongController : ControllerBase
{
        [HttpPost("[action]")]
        public string Ping(string msg)
        {
            return msg == "Ping" ?  "Pong" : "Bad";
        }
}

<button class="btn btn-primary" @onclick="Ping">@ButtonName</button>

@code{

	[Inject]
	HttpClient Http { get; set; }

	private string ButtonName { get; set; } = "Ping";

	private async Task Ping()
	{
		Http.BaseAddress = new Uri("https://localhost:44321/");
		StringContent stringContent = new StringContent("Ping", System.Text.Encoding.UTF8);
		var result = await Http.PostAsync("api/PingPong/Ping", stringContent);

		ButtonName = await result.Content.ReadAsStringAsync();

	}
}