How to resolve "TypeError: Failed to fetch" error on Blazor?

 Unhandled exception rendering component: TypeError: Failed to fetch

WebAssembly.JSException: TypeError: Failed to fetch

I did a test to make request(s) from my Blazor WebAssembly app to action method with testing data, which works well on my side.

[Route("[controller]")]
[ApiController]
public class CustomerController : ControllerBase
{
    [HttpGet]
    [Route("GetAllCustomers")]
    public async Task<IEnumerable<Customer>> GetAllCustomersAsync()
    {
        //for testing purpose

        return new List<Customer> { new Customer { Id = 1, Name = "Test1" }, new Customer { Id = 2, Name = "Test2" } };

        //return await _service.GetAllCustomersAsync();
    }
}

GetAllCustomers.razor

@page "/getallcustomers"
@using BlazorWasmApp1.Shared
@inject HttpClient _httpClient

<h3>Customer List</h3>

@if (customers == null)
{
    <p><em>Loading...</em></p>
}
else
{
    <table class="table">
        <thead>
            <tr>
                <th>Id</th>
                <th>Name</th>
            </tr>
        </thead>
        <tbody>
            @foreach (var customer in customers)
            {
                <tr>
                    <td>@customer.Id</td>
                    <td>@customer.Name</td>
                </tr>
            }
        </tbody>
    </table>
}


@code {
    private Customer[] customers;

    protected override async Task OnInitializedAsync()
    {
        //call external API
        //_httpClient.BaseAddress = new Uri("https://localhost:44312/");


        //your API action would return a collection of Customer
        //you can try to call .GetFromJsonAsync<Customer[]>() to get the expected data
        //rather than get stream
        customers = await _httpClient.GetFromJsonAsync<Customer[]>($"Customer/GetAllCustomers");
    }
}

Test Result

To troubleshoot the issue, please try:

1. check the URL of your request in browser developer tool Network tab, and make sure you are making request to correct endpoint

2. if your ASP.NET Core Web API project is hosting on separate site, please make sure you configured and enabled CORS to allow request(s) from your Blazor WebAssembly app, and make sure that API is running