Angular: Getting a field is requested error for a non-null field

I try to create a webpage to my webshop and upload to the database

OnSubmit(): void {
const formData = new FormData();

formData.append('Language', 'en');
formData.append('Token', 'dfdfbsbfuefnbyxvfg6327jf843i');
formData.append('Domain', 'localhost');

formData.append('WebPageName', this.website.WebPageName);
formData.append('Company_ID', this.website.CompanyId.toString());
formData.append('CountryId', this.website.CountryId.toString());
formData.append('LanguageId', this.website.LangId.toString() || '0');

formData.append('CssBasics', this.website.CssBasic || '0');
formData.append('HTMLCode', this.website.HTMLCode || '0');

this.apiService.postMultipart('Domain/adddomain', formData).subscribe(
res => {
console.log('domain saved successfully:', res);
this.loadWebPages();
},
err => console.error('Error saving domain:', err)
);
}


It should load this DTO:

public int ID { get; set; }
public string WebPageName { get; set; }
public string? Comments { get; set; }
public DateTime? Created_At { get; set; }
public DateTime? Updated_At { get; set; }
public int Company_ID { get; set; }
public int CountryId { get; set; }
public int LanguageId { get; set; }
public string? CssBasics { get; set; }
public string? HTMLCode { get; set; }


In my payload all the required fields are non-null, which looks good to me, but i getting this response image

Currently I am fully out of ideas why this is happening since I named exactly the same and it should not be null

Edit: The Controller part of the code:

[HttpPost("adddomain")]
public async Task<IActionResult> AddDomain([FromForm] WebPage domain)
{
domainModule = new BIDomain(1, _configuration);

if (!ModelState.IsValid)
{
return BadRequest(ModelState);
}

try
{
// A ProductModule AddProductAsync metódusának meghívása
bool result = await domainModule.AddDomainAsync(domain);

if (result)
{
return Ok(new { Message = "Termék sikeresen hozzáadva!" });
}

return StatusCode(StatusCodes.Status500InternalServerError, "Nem sikerült hozzáadni a terméket.");
}
catch (Exception ex)
{
// Hiba esetén 500-as válasz
return StatusCode(StatusCodes.Status500InternalServerError, new { Error = ex.Message });
}
}

Continue reading...