add_action('wp_ajax_test_api_credentials', 'test_api_credentials');

function test_api_credentials() {
    $credentials = json_decode(get_option('dmca_solve_google_api_credentials'), true);
    if (empty($credentials)) {
        echo 'No API credentials provided.';
        wp_die();
    }

    require_once plugin_dir_path(__FILE__) . 'google-api-php-client/src/Google_Client.php';

    $client = new Google_Client();
    $client->setAuthConfig($credentials);

    try {
        $client->fetchAccessTokenWithAssertion();
        if ($client->getAccessToken()) {
            echo 'API credentials are valid.';
        } else {
            echo 'Failed to authenticate with provided credentials.';
        }
    } catch (Exception $e) {
        echo 'Error: ' . $e->getMessage();
    }

    wp_die();
}
<br />
<b>Warning</b>:  Constant WP_DEBUG already defined in <b>/home/fikfap/public_html/wp-config.php</b> on line <b>88</b><br />
<br />
<b>Warning</b>:  Constant WP_DEBUG_LOG already defined in <b>/home/fikfap/public_html/wp-config.php</b> on line <b>89</b><br />
<br />
<b>Warning</b>:  Constant WP_DEBUG_DISPLAY already defined in <b>/home/fikfap/public_html/wp-config.php</b> on line <b>90</b><br />
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