How do you handle business errors and return correct HTTP codes to the client?

To handle business errors and return correct HTTP status codes in C#, custom exceptions and middleware or filters for centralized error handling are usually used.

Example approach:

1. Create your own exception classes for different types of business errors:

public class NotFoundException : Exception {}
public class ValidationException : Exception {}

2. Throw these exceptions in controllers when necessary.

3. Use middleware to intercept exceptions and generate HTTP responses:

app.Use(async (context, next) => {
    try
    {
        await next();
    }
    catch (NotFoundException)
    {
        context.Response.StatusCode = StatusCodes.Status404NotFound;
        await context.Response.WriteAsync("Resource not found");
    }
    catch (ValidationException ex)
    {
        context.Response.StatusCode = StatusCodes.Status400BadRequest;
        await context.Response.WriteAsync(ex.Message);
    }
    catch (Exception)
    {
        context.Response.StatusCode = StatusCodes.Status500InternalServerError;
        await context.Response.WriteAsync("Internal server error");
    }
});

Thus, business logic is separated from HTTP processing, and the client receives understandable and correct response codes depending on the situation.