“mail” attribute is expected, but missing, in SAML response.

Hello everyone,
I’m currently learning how to setup an SAML IDP (SimpleSAMLPHP) and SAML SP (WordPress). Currently I still can’t login to the WordPress, it keep saying: “”mail” attribute is expected, but missing, in SAML response.”
I believe it is related to attribute, and metadata. But I still can’t firgue out how to fix it.

Here is the saml20-sp-remote.php file:

$metadata['https://xyz.com'] = [
    'AssertionConsumerService' => 'https://xyz.com/wp-login.php',
    'SingleLogoutService' => 'https://xyz.com/',
    'NameIDFormat' => 'urn:oasis:names:tc:SAML:1.1:nameid-format:emailAddress',
    'simplesaml.nameidattribute' => 'mail',
    'simplesaml.attributes' => true,
    'attributes' => array('mail', 'cn', 'uid'),
];

Here is the AuthData from SimpleSAMLPHP demo:

{
    "Attributes": {
        "uid": [
            "john"
        ],
        "cn": [
            "John Doe"
        ],
        "mail": [
            "[email protected]"
        ],
        "password": [
            "1@^%&!()S(Ae8912938192839t9?w9389812938"
        ]
    },
    "AuthnInstant": 1601778090,
    "Expire": 1601806890
}

Here is the attribute mapping configs:

user_login => uid
user_mail => mail
display_name => cn
first_name => cn
last_name => ''

Thank you for taking your time to help me. If you need any further information, just let me know!