So I’m trying to add in the database certain items into a user stock, and I get this problem
For context I’m using .netcore web api, entityframework, identity and sql server on backend and reactjs in the frontend.

using EasyLink.Server.Database.DbModels;
using EasyLink.Server.Database.DbModels.User;
using EasyLink.Server.Identity;
using EasyLink.Server.Models.Categories.Stock;
using EasyLink.Server.Validations.CamelCaseConcat;
using Microsoft.AspNetCore.Identity;
using System.Security.Claims;

namespace EasyLink.Server.Services.Stock
{
    public class StockService : IStockService
    {
        private readonly UserManager<ApplicationUser> _userManager;

        public StockService(UserManager<ApplicationUser> userManager)
        {
            _userManager = userManager;

        }
    

        public async Task<bool> StockAddData(StockDataRequest request, ClaimsPrincipal User)
        {
            try
            {

                var userIdClaim = User.Claims.FirstOrDefault(c => c.Type == ClaimTypes.NameIdentifier);
                if (userIdClaim == null)
                {
                    Console.WriteLine("User ID claim not found.");
                    return false;
                }

                var userId = userIdClaim.Value;

                var currentUser = await _userManager.FindByNameAsync(userId);

                if (currentUser!.Stock == null)
                {
                    Console.WriteLine("Stock is null. Initializing stock.");
                    currentUser.Stock = new StockModel
                    {
                        ApplicationUserId = currentUser.Id,
                        AutoParts = new List<AutoPart>()
                    };
                }
                string fieldName = CamelCase.ConvertToCamelCase(request.Field!);
                if (request.Field == "Anvelope" && request.Data!.Categories!.ContainsKey(fieldName))
                {
                    var tyreDataJson = request.Data.Categories[fieldName]?.ToString();
                    if (string.IsNullOrEmpty(tyreDataJson))
                    {
                        Console.WriteLine("Tyre data is null or empty.");
                        return false;
                    }
                    var tyreData = CamelCase.DeserializeJsonCamel<AnvelopeModel>(tyreDataJson);

                    if (tyreData == null)
                    {
                        Console.WriteLine("Failed to deserialize tyre data.");
                        return false;
                    }


                    // Handle potential null values by providing defaults
                    var newAnvelope = new Anvelope
                    {
                        VehicleType = request.Data.Mandatory?.TipVehicul,
                        PartType = request.Data.Mandatory?.TipPiesa,
                        Delivery = request.Data.Mandatory?.Nou,
                        IsNew = request.Data.Mandatory?.Nou,
                        Price = request.Data.Mandatory?.Pret != null ? Convert.ToInt32(request.Data.Mandatory.Pret) : (int?)null,
                        Tva = request.Data.Mandatory?.Negociabil,
                        IsNegotiable = request.Data.Mandatory?.Negociabil,
                        Stock = currentUser.Stock,
                        TipDeAnvelope = Enum.TryParse<TyreType>(tyreData.TipDeAnvelope, out var tyreType) ? tyreType : TyreType.ToateSezoanele,
                        EmisieDeZgomot = tyreData.EmisieDeZgomot,
                        AderentaPeUmezeala = tyreData.AderentaPeUmezeala,
                        EficientaInCombustibil = tyreData.EficientaInCombustibil,
                        LatimeAnvelope = tyreData.LatimeAnvelope,
                        Producator = tyreData.Producator
                    };

                    currentUser.Stock!.AutoParts!.Add(newAnvelope);
                }
                else
                {
                    Console.WriteLine("Field is not 'Anvelope' or data is missing.");
                    return false;
                }

                // Save changes to the database
                Console.Write("nnnnnn1111nnnnn");//this writes 1111
                var updateResult = await _userManager.UpdateAsync(currentUser);
                if (!updateResult.Succeeded)
                {
                    Console.WriteLine($"Failed to update user: {string.Join(", ", updateResult.Errors.Select(e => e.Description))}");
                    return false;
                }

                return true;
            }
            catch (Exception ex)
            {
                Console.WriteLine($"Exception occurred: {ex.Message} {ex.Source}");
                return false;
            }
        }




    }
}

this is from the client-side:

const sendForm = async () => {
    const formErrors = [];
    const formKeys = Object.keys(formData.mandatory);
    formKeys.forEach((e) => {
        if (formData.mandatory[e] === "") formErrors.push(e);
    });
    setError(formErrors);

    if (formErrors.length === 0) {
        const field = main.partType.data[currentCategoryIndex];
        try {
            console.log("sent");
            const response = await fetch('https://localhost:7128/api/stock/StockAddData', {
                method: 'POST',
                headers: {
                    'Content-Type': 'application/json'
                },
                credentials: 'include',
                body: JSON.stringify({
                    Data: formData,
                    Field: field
                })
            });

            if (response.ok) {
                console.log("RIGHT");
            } else {
                throw new Error('Failed to send data');
            }
        } catch (error) {
            console.error('Error sending data:', error);
        }
    }
};

I expected the service to return true, but it returns false and the error I mentioned.