Why does Ef Core not save my data in the database?

public async Task<WebshopPoco?> CreateOrderAsync(WebshopPoco order)
{
    this.Logger.TraceMethodBegin();

    if (order == null)
    {
        throw new ArgumentNullException(nameof(order));
    }
    this.Logger.LogDebug($"Method parameter 'objectPoco': {order}");

    try
    {
        this.Context.Entry(order).State = EntityState.Added;
        this.Context.Entry(order.Contact).State = EntityState.Added;
        this.Context.Entry(order.Contact?.Address).State = EntityState.Added;
        this.Context.Entry(order.WebshopBillingInfoPoco).State = EntityState.Added;
        this.Context.Entry(order.WebshopBillingInfoPoco?.Address).State = EntityState.Added;

        if (order.Items != null)
        {
            foreach (var item in order.Items)
            {
                order.Id = 0;

                this.Context.Entry(item).State = EntityState.Added;
            }
        }

        return await this.Context.SaveChangesAsync() >= 1 ? order : null;
    }

    catch (Exception e)
    {
        this.Logger.LogError(e.Message);
        return null;
    }
    finally
    {
        Logger.TraceMethodEnd();
    }
}