htaccess external domain to new domain - wordpress

Question

I have asked my domain host provider to point a website to my public_html folder. but now I have been told the if I need this other domain to redirect to a particular url on my primary domain website, I would need to do it in the htaccess file. At the moment I have researched and this is what my htaccess looks like without any luck!
# Switch rewrite engine off in case this was installed under HostPay.
RewriteEngine Off
SetEnv DEFAULT_PHP_VERSION 5
DirectoryIndex index.cgi index.php
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress
RewriteCond %{HTTP_HOST} ^otherdomain.org.uk
RewriteRule ^(.*)$ http://www.primarydomain.org/blog/$1 [R=permanent,L]
The above does not redirect my otherdomain.org.uk to the blog page on my primarydomain.org/blog. Please note that my primarydomain.org/blog is a wordpress website page.

Answer 1

Keep redirect rules before your WP rules.
Have your rules like this:
# Switch rewrite engine off in case this was installed under HostPay.
RewriteEngine Off
SetEnv DEFAULT_PHP_VERSION 5
DirectoryIndex index.cgi index.php
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{HTTP_HOST} ^otherdomain.org.uk
RewriteRule ^(.*)$ http://www.primarydomain.org/blog/$1 [R=permanent,L]
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress