Two different installs: Login once (share cookies)

Hi folks,

I knooooow many before me have had, asked about and gotten answers to this issue ..but some are for older versions of WP, and I JUST can’t get this to work ??

Situation: I have two *different installs (WP1 and WP2)of WP on the same domain running on the same database using different prefixes.
*different = WP2 is a backupbuddy backup of WP1.

Need: To be able to login ONCE on eiter WP1 or WP2 and to then be logged into both.

Problem: I have tried “everything”, but I just can’t get it to work! Salts are the same in wp-config.php for WP1 and WP2.

This is the wp-config.php of WP2. Values are changed to dummy values:

<?php
/**
 * The base configurations of the WordPress.
 *
 * This file has the following configurations: MySQL settings, Table Prefix,
 * Secret Keys, WordPress Language, and ABSPATH. You can find more information
 * by visiting {@link https://codex.www.ads-software.com/Editing_wp-config.php Editing
 * wp-config.php} Codex page. You can get the MySQL settings from your web host.
 *
 * This file is used by the wp-config.php creation script during the
 * installation. You don't have to use the web site, you can just copy this file
 * to "wp-config.php" and fill in the values.
 *
 * @package WordPress
 */

// ** MySQL settings - You can get this info from your web host ** //
/** The name of the database for WordPress */
define('DB_NAME', 'wp_db');

/** MySQL database username */
define('DB_USER', 'wp_user');

/** MySQL database password */
define('DB_PASSWORD', 'password');

/** MySQL hostname */
define('DB_HOST', 'something.unoeuro.com:');

/** Database Charset to use in creating database tables. */
define('DB_CHARSET', 'utf8');

/** The Database Collate type. Don't change this if in doubt. */
define('DB_COLLATE', '');

/**#@+
 * Authentication Unique Keys and Salts.
 *
 * Change these to different unique phrases!
 * You can generate these using the {@link https://api.www.ads-software.com/secret-key/1.1/salt/ www.ads-software.com secret-key service}
 * You can change these at any point in time to invalidate all existing cookies. This will force all users to have to log in again.
 *
 * @since 2.6.0
 */
define('AUTH_KEY',         'salt1');
define('SECURE_AUTH_KEY',  'salt2');
define('LOGGED_IN_KEY',    'salt3');
define('NONCE_KEY',        'salt4');
define('AUTH_SALT',        'salt5');
define('SECURE_AUTH_SALT', 'salt6');
define('LOGGED_IN_SALT',   'salt7');
define('NONCE_SALT',       'salt8');
/**#@-*/

/**
 * WordPress Database Table prefix.
 *
 * You can have multiple installations in one database if you give each a unique
 * prefix. Only numbers, letters, and underscores please!
 */
$table_prefix  = 'wp1_';

/**
 * WordPress Localized Language, defaults to English.
 *
 * Change this to localize WordPress. A corresponding MO file for the chosen
 * language must be installed to wp-content/languages. For example, install
 * de_DE.mo to wp-content/languages and set WPLANG to 'de_DE' to enable German
 * language support.
 */
define ('WPLANG', 'da_DK');

/**
 * For developers: WordPress debugging mode.
 *
 * Change this to true to enable the display of notices during development.
 * It is strongly recommended that plugin and theme developers use WP_DEBUG
 * in their development environments.
 */
define('WP_DEBUG', false);

$root_host = 'mysite.com';
define( 'COOKIE_DOMAIN', '.'.$root_host );
define( 'COOKIEHASH', md5('https://'.$root_host) );

/* That's all, stop editing! Happy blogging. */

/** Absolute path to the WordPress directory. */
if ( !defined('ABSPATH') )
	define('ABSPATH', dirname(__FILE__) . '/');

/** Sets up WordPress vars and included files. */
require_once(ABSPATH . 'wp-settings.php');

I’ve alto tried:

$cookiehash = md5("https://uniqture.dk");  // Use Site A's URL

define(CUSTOM_USER_TABLE,'uniqture_users');           //Change 'wp' to match the prefix set during
define(CUSTOM_USER_META_TABLE,'uniqture_usermeta');   //  Site A's installation
define('COOKIEPATH', '/');                      //This path should reference Site A's root
define('SITECOOKIEPATH', '/');                  //Should match 'COOKIEPATH'
define('COOKIEHASH', $cookiehash );

Can anyone help me getting this t work? It’s probably simple as heck ..but I just can’t get this important “little” thing to do as I want it to ??

(..and no, a multisite is not a solution for me, as I need an exact copy of my main site, whis will take me forever to recreate + need 100% control when editing both sites)

Thanks a lot in advance for any help! ??

[ No bumping please. ]