Users cannot login to Secondary Sites – I NEED HELP ASAP!

Hi all. I’m an average web developer and this issue it’s driving me crazy. I googled on this everyday for about two weeks now. I’m about to hang myself! LOL

I have a Network (Subdiretories type) running on the following structure:

Domain: https://www.domain.com (Not a WP site)
WP files: https://www.domain.com/wp/
Primary WP Site: https://www.domain.com/wp/ (Same location as WP files)
Secondary WP Sites: https://www.domain.com/wp/Site2/, https://www.domain.com/wp/Site3/ and https://www.domain.com/wp/Site4/
Hosting: GoDaddy (Windows Server)

This is what is happening:

1. I can access both the network dashboard and the sites. Aparently, all is working fine here, since I can setup the sites (Primary and Secondaries) and navigate as a visitor without any problem.

2. As a User, I can ONLY signup, login and/or comment on the Primary Site.

3. As a User, I CANNOT SIGNUP, LOGIN AND/OR COMMENT ON ANY SECONDARY WP SITES. When I try to do any of those procedures on any of the secondary WP sites, I just get redirected to the homepage of the secondary site.

4. When I login as a User on the Primary Site, it seems like I’m logging into the whole Network (the welcome message says “Welcome to the Network”) instead of logging into the Primary Site, but once logged, I can only comment on the primmary WP Site, but when I go to any secondary WP site (I can see at the top that the User is still logged), when I try to comment, I just get redirected to that site’s homepage (as said before).

5. When I login to the Network or the Primary WP Site AS ADMIN, I can only comment on the primary WP Site, but when I try to comment on any secondary WP Site, I face the same issue.

This is what my web.config looks like:

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
	<system.webServer>
		<rewrite>
			<rules>
				<rule name="WordPress Rule 1" stopProcessing="true">
					<match url="^index\.php$" ignoreCase="false" />
					<action type="None" />
				</rule>
				<rule name="WordPress Rule 2" stopProcessing="true">
					<match url="^([_0-9a-zA-Z-]+/)?wp-admin$" ignoreCase="false" />
					<action type="Redirect" url="{R:1}wp-admin/" redirectType="Permanent" />
				</rule>
				<rule name="WordPress Rule 3" stopProcessing="true">
					<match url="^" ignoreCase="false" />
					<conditions logicalGrouping="MatchAny">
						<add input="{REQUEST_FILENAME}" matchType="IsFile" ignoreCase="false" />
						<add input="{REQUEST_FILENAME}" matchType="IsDirectory" ignoreCase="false" />
					</conditions>
					<action type="None" />
				</rule>
				<rule name="WordPress Rule 4" stopProcessing="true">
					<match url="^" ignoreCase="false" />
					<conditions logicalGrouping="MatchAny">
						<add input="{REQUEST_FILENAME}" matchType="IsFile" ignoreCase="false" />
						<add input="{REQUEST_FILENAME}" matchType="IsDirectory" ignoreCase="false" />
						<add input="{URL}" pattern="([a-zA-Z0-9\./_-]+)\.axd" />
					</conditions>
					<action type="None" />
				</rule>
				<rule name="WordPress Rule 5" stopProcessing="true">
					<match url="^[_0-9a-zA-Z-]+/(wp-(content|admin|includes).*)" ignoreCase="false" />
					<action type="Rewrite" url="{R:1}" />
				</rule>
				<rule name="WordPress Rule 6" stopProcessing="true">
					<match url="." ignoreCase="false" />
					<action type="Rewrite" url="index.php" />
				</rule>
				<rule name="WordPress Rule 7" stopProcessing="true">
					<match url="^([_0-9a-zA-Z-]+/)?(.*\.php)$" ignoreCase="false" />
					<action type="Rewrite" url="{R:2}" />
				</rule>
			</rules>
		</rewrite>
		<httpRedirect enabled="false" destination="https://www.yourdomain.com" />
	</system.webServer>
</configuration>

This is what my wp-config.php looks like:

define('WPLANG', 'es_ES');

define('WP_DEBUG', true);
define('WP_ALLOW_MULTISITE', true);
define('MULTISITE', true);
define('SUBDOMAIN_INSTALL', false);
define('DOMAIN_CURRENT_SITE', 'domain.com');
define('PATH_CURRENT_SITE', '/wp/');
define('SITE_ID_CURRENT_SITE', 1);
define('BLOG_ID_CURRENT_SITE', 1);
define('ADMIN_COOKIE_PATH', '/');
define('COOKIE_DOMAIN', '');
define('COOKIEPATH', '');
define('SITECOOKIEPATH', '');
define('WP_HOME','https://www.domain.com/wp');
define('WP_SITEURL','https://www.domain.com/wp');
define('DISALLOW_FILE_EDIT', false);

Note: I use domain masking setup from the hosting cpanel, but I guess this is not relevant, since the issue described above behave the same way no matter if I access using the mask (i.e. site2domainmask.com) or not (i.e. domain.com/wp/site2).