fallBackResource not working in subdomain

fallBackResource not working in subdomain

I have an .htaccess file in /pages with a fallBackResource set to
/pages/index.php and it is working fine. This is my .htaccess file:
CheckSpelling off
FallbackResource /pages/index.php
When i looked up how to set up a fallBackResource the documentation i read
actually suggested to do it this other way:
<Directory /web/example.com/htdocs/blog>
FallbackResource /blog/index.php
</Directory>
Which i never managed to get working (500 internal server error) - until i
simply wrote FallbackResource /pages/index.php and then it worked well.
Now i want to do the same in a subdomain (the subdomain points to the
folder /forma) but of course nothing works. This is what i tried:
FallbackResource /forma/pages/index.php
And this .htaccess file is placed inside /forma/pages
Any hints?