I've created an .htaccess file that contains redirects for one site that is part of a larger WordPress Multisite install.
The .htaccess content starts with this (necessary because the same .httacess file must be used for multiple sites:
RewriteCond %{HTTP_HOST} ^mydomain.com [nc]
And then contains a series of rewrites, like so:
RewriteRule ^about-my-site$ about [R=301,NC,L]
If I visit mydomain.com/about-my-site
, I am correctly redirected to mydomain.com/about
However, if I visit mydomain.com/about-my-site/
(please note trailing slash), I get a "Page not found" error.
Change your RewriteRule to
RewriteRule ^about-my-site/?$ about [R=301,NC,L]