Process ModelState errors from WebAPI Blazor (server-side) call - asp.net-core-webapi

Question

When I am making a WebAPI call I want to find out how to pass back ModelState errors to my Blazor application.
The DataAnnotations all validate correctly but, if I do any other types of validation (once past the ModelState.IsValid call), I can't get those errors that I add to the ModelState to pass back to Blazor. What am I missing?
Blazor page
...
<EditForm Model="#_user" OnValidSubmit="#Update">
<DataAnnotationsValidator />
<ValidationSummary />
<div class="container">
<div class="row">
<div class="col-md-3">Name:</div>
<div class="col-md-9"><InputText id="Name" #bind-Value="#_user.UserName" class="form-control" /></div>
</div>
#if (_user.isNew)
{
<div class="row">
<div class="col-md-3">Password:</div>
<div class="col-md-9"><InputText id="Name" #bind-Value="#_user.Password" class="form-control" type="password" /></div>
</div>
<div class="row">
<div class="col-md-3">Validate your password:</div>
<div class="col-md-9"><InputText id="Name" #bind-Value="#_user.ValidatePassword" class="form-control" type="password" /></div>
</div>
}
<div class="row">
<div class="col-md-3">Email:</div>
<div class="col-md-9"><InputText id="Name" #bind-Value="#_user.Email" class="form-control" /></div>
</div>
<div class="row">
<div class="col-md-3">Roles:</div>
<div class="col-md-9">
#foreach (IdentityRole role in _roles)
{
bool isChecked = _user.UserRoles.Any(r => r.Id == role.Id);
<input type="checkbox" Id="#role.Id" name="#role.Id"
Class="form-control" checked="#isChecked" #onchange="#(e => RoleChecked(e, role.Id))" />
#role.Name
}
</div>
</div>
<button type="submit" class="btn btn-#buttonClass">#buttonText</button>
</div>
</EditForm>
}
#functions {
[Parameter]
string id { get; set; } = "";
private UserViewModel _user { get; set; }
...
private async Task Update()
{
if (id != "")
{
await apiClient.UpdateUserAsync(_user);
}
else
{
await apiClient.AddUserAsync(_user);
}
UriHelper.NavigateTo("admin/users");
}
...
WebAPI Controller
[HttpPost]
public async Task<IActionResult> Post([FromBody] UserViewModel applicationUser)
{
if (applicationUser == null)
{
_logger.LogError($"ApplicationUser object null");
return BadRequest("ApplicationUser object is null");
}
if (!ModelState.IsValid)
{
_logger.LogWarn("ApplicationUser object invalid");
return BadRequest(ModelState);
}
else
{
_logger.LogDebug($"Creating ApplicationUser {applicationUser.UserName}");
var obj = new ApplicationUser();
obj.Map(applicationUser);
IdentityResult result = await _userManager.CreateAsync(obj, applicationUser.Password);
if (result.Succeeded)
{
//put the newly created user back on top of the parameter for role creation
applicationUser.Map(obj);
await IdentityHelpers.UpdateUserRoles(_userManager, applicationUser);
return CreatedAtRoute("", new { id = applicationUser.Id }, applicationUser);
}
else
{
_logger.LogWarn("ApplicationUser object could not be created");
result.Errors.ToList().ForEach(e => ModelState.AddModelError(e.Code, e.Description));
return BadRequest(ModelState);
}
}
}
How do I pass back ModelState errors to Blazor so that it will respond to those in the same way that it would DataAnnotations (or model validation)?