Cannot call Blazor hosted API due to CSP

I've got the following API Controller:

[ApiController][Route("api")]public class ItemsController : Controller{  private readonly ApplicationDbContext _context;  public ItemsController(ApplicationDbContext context)  {    _context = context;  }  [HttpGet("Items")]  public IEnumerable<Item> Get()  {    var items = _context.Items.ToArray();    return items;  }  [HttpPost("Item")]  public async Task<ActionResult> UpdateEmployee(Item item)  {    try    {        _context.Items.Add(item);        var res = await _context.SaveChangesAsync();        if (res > 0)            return Ok();        else return StatusCode(StatusCodes.Status500InternalServerError);    }    catch (Exception ex)    {        return StatusCode(StatusCodes.Status500InternalServerError,"Error updating data");    }  }}

I can call the GET method from Firefox no problem but when I try to call the POST method I get an error about violating "default-src 'none'".

I have then added the following:

app.Use(async (context, next) =>{  context.Response.Headers.Append("Content-Security-Policy", "default-src * 'unsafe-inline''unsafe-eval'; script-src * 'unsafe-inline''unsafe-eval'; connect-src * 'unsafe-inline'; img-src * data: blob: 'unsafe-inline'; frame-src *; style-src * 'unsafe-inline';");  await next();});

But now I get a non-expressive json+problem response and the code is not executed.

I do not know how to proceed from here.