I originally used plain port forwarding to reach Tiny Tiny RSS from outside the local network. It was easy to set up, but after spending some time on it, switching to FRP made more sense. The main advantage is obvious: no direct port exposure, which is safer. The tradeoff is that the configuration needs a bit more care.

The key setting is the TT-RSS self URL.

SELF_URL*PATH should point to:

https:// your_domain/1281/ttrss/

In the config.php file under FileStation -> Web -> rss, line 21 needs to be adjusted to:

define('SELF_URL_PATH', 'https://your_domain:1281/ttrss/');

This turned out to be the critical part of the whole setup.

What finally solved it was changing the way TT-RSS was exposed internally on Synology. In Web Station, create a virtual host and assign an additional port so TT-RSS can be accessed directly through a local address, something like 192.168.1.1:3333.

After that, go back to config.php in FileStation -> Web -> rss and modify line 21 again to:

define('SELF_URL_PATH','ttrss.yourname.com');

Once that was in place, FRP could proxy it correctly and the service became directly accessible from the public internet.