Firefly III won't run under a sub-folder (reverse-proxy path)¶

You try to serve Firefly III behind a reverse proxy at a path like https://host/firefly/, alongside other apps on the same domain. Pages load broken — missing CSS, wrong redirects, links pointing at the domain root.

Cause¶

Firefly III does not support running from a sub-directory. It builds absolute, root-relative URLs from APP_URL, assuming it lives at the root of a (sub)domain. Under /firefly/, its own links and assets resolve to /… instead of /firefly/….

What works instead¶

• A dedicated (sub)domain at root — e.g. firefly.host, proxied to the container, with APP_URL=https://firefly.host. This is the supported layout.
• Its own port/host at root (no path prefix), if you'd rather not add a subdomain.

Set TRUSTED_PROXIES=** (or your proxy's IP) so Firefly honours X-Forwarded-* headers, and make APP_URL match exactly how you reach it.

Takeaway¶

Path-based reverse proxying (/app/) works for many self-hosted apps — but not Firefly III. Give it a subdomain or a dedicated host root.