Troubleshooting

Start with the logs: docker compose logs toppo tells what Toppo did and, when it fails, why.

What happens	What to do
The setup code is lost	Restart Toppo (docker compose restart toppo): it prints a new one until setup is done.
Toppo does not start	The logs say why: an unknown or invalid TOPPO_* variable, a database that cannot be reached, a migration that failed (the database is then left as it was).
/health answers 503	Toppo runs but cannot reach its database: check docker compose ps and the logs of db.
Links in emails point to the wrong address	Set TOPPO_URL to the address people open, then docker compose up -d.
No email arrives	Send a test message from Settings › Email: it says what went wrong, the connection, TLS, the account or the message refused. Check the spam folder, and that the sender address may send through that server.
Everyone was signed out after a move	The /data volume, with its secret key, was not moved along: restore it, or set TOPPO_SECRET yourself. Enter the mail password again in Settings › Email.
Attachments fail behind the proxy	The proxy refuses large requests: let it accept the size of TOPPO_ATTACHMENT_MAX_SIZE_MB (nginx: client_max_body_size).
Sign-ins are refused as too many	Behind a reverse proxy, Toppo sees every client at the proxy's address until TOPPO_TRUST_PROXY=true (the client's address).
The interface speaks the wrong language	Each person chooses theirs in My account › Language; emails follow it.

Still stuck? Open an issue with the version (bottom of the sidebar) and what the logs say. A security problem is reported privately, as SECURITY.md explains.