HTTP/HTTPS redirect issues

I am having a similar problem and this addition to the .htaccess file has not resolved it.

The difference may be that I am using the Really Simple SSL plugin which already has similar code in the .htaccess file (see code below). I need both plugins to work together.

My problem:
When a browser goes to http://www.domainA.com it is redirected to https://www.domainA.com
When a browser goes to http://www.domainB.com it is redirected to https://www/domainB.com

However, when I have set up a redirect on the Multiple Domain Mapping on a Single Site plugin that redirects a specific URL on domainB to a page on domainA, this only works if the browser requests the HTTPS version of the page. When the HTTP version is requested then it returns file not found.

Example:
Multiple Domain Mapping on a Single Site maps:
domainB.com/product –> domainA.com/content/page1

https://domainB.com/product displays correctly
http://domainB.com/product redirects to https://domainB.com/content/page1 and gives a 404 message

Really Simple SSL .htaccess code:

# BEGIN rlrssslReallySimpleSSL rsssl_version[3.2.9]
<IfModule mod_rewrite.c>
RewriteEngine on
RewriteCond %{HTTPS} !=on [NC]
RewriteRule ^(.*)$ https://%{HTTP_HOST}/$1 [R=301,L]
</IfModule>
# END rlrssslReallySimpleSSL
# BEGIN Really_Simple_SSL_SECURITY_HEADERS
<IfModule mod_headers.c>
Header always set X-XSS-Protection “1; mode=block”
Header always set X-Content-Type-Options “nosniff”
Header always set Referrer-Policy: “no-referrer-when-downgrade”
</IfModule>
# END Really_Simple_SSL_SECURITY_HEADERS

Your help would be much appreciated.