How do I return complex object in POST request response body

public async Task<AppUser> CreateUser(AppUser user, RegisterUserDto dto)
        {
            try
            {
                var result = await _userManager.CreateAsync(user, dto.Password);
                if (result.Succeeded)
                {
                    await _userManager.AddToRoleAsync(user, "Member");
                    await _context.SaveChangesAsync();
                    return user;
                }
                return null;
                
            }
            catch (Exception ex)
            {
                _logger.LogError("Error at AuthRepository at CreateUser, ex:" + ex.StackTrace, false);
            }
            return null;
        }

[HttpPost]
  [Route("createuser")]
  public async Task<IActionResult> CreateUserAcc([FromBody] RegisterUserDto userDto)
  {
      try
      {
          var identity = _mapper.Map<AppUser>(userDto);
          var result= await _repository.CreateUser(identity, userDto);
          if (result!=null)
              return Ok(result);
          else
              return BadRequest("Account alredy exists.");
      }
      catch (Exception)
      {

      }
      return BadRequest();
  }