How to login and create JWT in symfony 4.4 in Ubuntu with detailed configuration?

Question

I used lexik/jwt-authentication-bundle.

security.yaml

security:
    encoders:
        # an encoder used in the past for some users
        legacy:
            algorithm: sha256
            encode_as_base64: false
            iterations: 1

        App\Entity\User:
            # the new encoder, along with its options
            algorithm: auto

    # https://symfony.com/doc/current/security.html#where-do-users-come-from-user-providers
    providers:
        # used to reload user from session & other features (e.g. switch_user)
        app_user_provider:
            entity:
                class: App\Entity\User
                property: email
        # used to reload user from session & other features (e.g. switch_user)
        # used to reload user from session & other features (e.g. switch_user)
    firewalls:
        login:
            pattern: ^/api/users/login
            stateless: true
            anonymous: true
            provider: app_user_provider
            json_login:
                check_path: api_login
                success_handler: lexik_jwt_authentication.handler.authentication_success
                failure_handler: lexik_jwt_authentication.handler.authentication_failure
        register:
            pattern: ^/api/users/register
            stateless: true
            anonymous: true
            provider: app_user_provider
            json_login:
                check_path: api_register
                success_handler: lexik_jwt_authentication.handler.authentication_success
                failure_handler: lexik_jwt_authentication.handler.authentication_failure
        api:
            pattern: ^/api
            stateless: true
            anonymous: false
            provider: app_user_provider
            guard:
                authenticators:
                    - lexik_jwt_authentication.jwt_token_authenticator
        dev:
            pattern: ^/(_(profiler|wdt)|css|images|js)/
            security: false

    access_control:
        - { path: ^/api/users/login, roles: IS_AUTHENTICATED_ANONYMOUSLY }
        - { path: ^/api/users/register, roles: IS_AUTHENTICATED_ANONYMOUSLY }

lexik_jwt_authentication.yaml

lexik_jwt_authentication:
    secret_key: '%kernel.project_dir%/config/jwt/private.pem'
    public_key: '%kernel.project_dir%/config/jwt/public.pem'
    pass_phrase: '%env(JWT_PASSPHRASE)%' # If using public/private key pair (optional)
    token_ttl: 3600 # Token Time-to-live (in seconds)

UserController.php

/**
     * @Route("/api/users/login", name="app_user_login", methods="POST")
     */
    public function login(Request $request): Response
    {
        $email = $request->request->get('email');
        $password = $request->request->get('password');
        $user = $this->getDoctrine()->getRepository(User::class)->findOneBy(['email' => $email]);
        if (!$user) {
            return $this->json(['message' => 'Invalid credentials'], 401);
        } else if (!$this->userPasswordEncoder->isPasswordValid($user, $password)) {
            return $this->json(['success' => false, 'msg' => 'Password Incorrect!']);
        }
        // Generate the JWT token
        $token = $this->jwtTokenManager->create($user);

        return $this->json([
            'token' => $token,
        ]);
    }

Test by Postman, and result is:

JWTEncodeFailureException
Unable to create a signed JWT from the given configuration.

How can I solve it?