Why doesn't this simple API call to ASP.net work within ReactJS?

Question

UsersController.cs

namespace testlol
{
    [ApiController]
    public class UsersController : ControllerBase
    {
        private readonly ILogger<UsersController> _logger;

        static readonly Models.IUserRepository repository = new Models.UserRepository();

        public UsersController(ILogger<UsersController> logger)
        {
            _logger = logger; //what is this ?
        }

        [HttpGet]
        [Route("api/users")]
        public IEnumerable<Models.UserModel> GetAllUsers()
        {
            return repository.GetAll();
        }

        [HttpPost]
        [Route("api/user")]
        [Consumes("application/json")]
        public Models.UserModel PostUser(Models.UserModel item)
        {
            return repository.Add(item);
        }
    }
}

Where I then use the service in react: userService.js

export async function getAllUsers() {
    const response = await fetch('/api/users');
    return await response.json();
}

Then, I try to call it in a component:

import { getAllUsers } from "../services/userService.js"
...
 useEffect(() => {
        const getUserList = () => {
            console.log("Getting user list ..");
            getAllUsers()
                .then(userList => {
                    console.log("User list: ")
           
                    console.log(userList)
                    setUsers(userList)
                });
        }
        getUserList()
    }, [])

This always yields the error: SyntaxError: JSON.parse: unexpected character at line 1 column 1 of the JSON data

I'm not sure how the program isn't working. I saw that it could be a blank string, but I'm also currently storing some hardcoded values in another file:

   public UserRepository()
        {
            Add(new UserModel { email = "[email protected]", password ="password" });
            Add(new UserModel { email = "[email protected]", password ="admin" });
        }