How to get the error I receive in the XHR responses

In my backend I have a series of validations when logging in. These validations return errors. I see these errors (from the frontend) in the chrome inspector, in the network tab, filtering the XHR (image).

The thing is that, if I loginput a in my front-end action try catch, the error that it catches (and I show on the console) does not have all the details. It just says Error: Network error: Response not successful: Received status code 500.

I want to show custom alerts and for this it would be good to be able to get the error as I am seeing it in the browser inspector .

Login in the backend

async loginUser(_, { input }) {
        const { errors, valid } = validateLoginInput(input.username, input.password)
        if (!valid) {
            return new UserInputError("Errores:", { errors })
        }
        let user = await User.findOne({ username: input.username })
        if (!user) {
            user = await User.findOne({ email: input.username })
            if (!user) {
                errors.general = "El usuario o e-mail ingresado no se encuentran registrados"
                return new UserInputError("Error de credenciales", { errors })
            }
        }

        const match = await bcrypt.compare(input.password, user.password)

        if (!match) {
            console.log("tengo errores en valid: ",errors)
            errors.general = "La contraseña es incorrecta."
            return new UserInputError("Error de credenciales", { errors })
        }


        const token = generateToken(user)

        return {
            ...user._doc,
            id: user._id,
            password: 'null',
            token
        }
    },

Login on the front end

async loginUser({ commit }, userData) {
    try {
        let { data: { loginUser } } = await apolloClient.mutate({
            mutation: LOGIN_USER,
            variables: userData
        })

        const user = {
            username: loginUser.username,
            email: loginUser.email,
            id: loginUser._id
        }

        const token = loginUser.token
        commit('loginUser', user)
        commit('setToken', token)
        localStorage.setItem('apollo-token', token)
        router.push('/inicio')
    } catch (err) { 
        console.log(err)
        // ACA QUIERO VER EL ERROR DE LA IMAGEN
    }
},

Does anyone know how to do that? I am using Vue 2 with Apollo. Thank you very much.