Web API With AJAX problem /Failed to load resource: the server responded with a status of 400 ()

[HttpPost("Login")]
        public async Task<IActionResult> Login([FromBody] SigninViewModel formData)
        {
            MemberCredential membercredential = await db.MemberCredential.FirstOrDefaultAsync(t => t.MemberAccount.Equals(formData.memberAccount));
        
                if (membercredential == null)
                {

                    var test = new { success = false, message = "無此帳號，請重新輸入。" };
                    Console.WriteLine(test);
                    return BadRequest(new { success = false, message = "無此帳號，請重新輸入。" });
                }
                bool isPwdMatch = BCrypt.Net.BCrypt.Verify(formData.memberPassword, membercredential.MemberPassword);
                
                Console.WriteLine("驗證結果：" + isPwdMatch);

                if (isPwdMatch == false)
                {
                    return BadRequest(new { success = false, message = "帳號或密碼錯誤，請重新輸入。" });
                
                }
            
       
                var LoginData = new
                {
                    MemberId = member.MemberId,
                    MemberName = member.MemberName,
                    MemberPoint = member.MemberPoint
                };
                string json = JsonSerializer.Serialize(LoginData);
                Console.WriteLine(json);
                HttpContext.Session.SetString(CDictionary.SK_LOINGED_USER, json);
                
                return Ok(new { success = true, message = "登入成功" });
            
            
        }

Enter the wrong password, and execute

return BadRequest(new { success = false, message = "帳號或密碼錯誤，請重新輸入。" });
this code, but ajax does not execute the action。

Failed to load resource: the server responded with a status of 400 ()

document.getElementById("Login").addEventListener("submit", function (event) {
            event.preventDefault();

            let MemberAccount = document.getElementById("MemberAccount").value;
            let MemberPassword = document.getElementById("MemberPassword").value;

            const formData=
            {
                memberAccount:MemberAccount,
                memberPassword:MemberPassword
            }

            $.ajax({
                type:"POST",
                url: "/api/Members/Login",
                data:JSON.stringify(formData),
                contentType: "application/json"
            }).done(data=>{
                if (data.success) {
                    alert("Login Success!");
                    window.location.href = "https://localhost:1111/Home/Index";
                } else {
                    alert("Login fail!");
                }
        }).fail((jqXHR, textStatus, errorThrown) => {
            console.error("AJAX error:", textStatus, errorThrown);
        });;

    });

If the login is successful, ajax will alert("Login Success!"),and
switch page to /Home/Index,but
the action about return BadRequest() is executed, but ajax does not make any action. In the developer's introduction, it appears that Failed to load resource: the server responded with a status of 400 (), please help me to modify the above program code, thank you!
enter image description here

public class SigninViewModel
{
    public string memberAccount { get; set; }
    public string memberPassword { get; set; }
}

When you return BadRequest() in backend, It will return 400 state code in response, So you need to handle it in fail() method. refer to this code:

.fail((jqXHR, textStatus, errorThrown) => {
            if (jqXHR.status === 400) {               
                const errorResponse = jqXHR.responseJSON; 
                alert(errorResponse.message); 
            } else {
                console.error("AJAX error:", textStatus, errorThrown);
            }
        });

Have you tried to use [FromBody] in the controller parameter.

The endpoint signature should be like this.

[HttpPost("Login")] public async Task<IActionResult> Login([FromBody]SigninViewModel scv)

If this not work defintely has to be related to the way you are sending the data from the frontend.

Please make us know if you try this.