Keep Tailscale turned on
Seedly reaches the server only while Tailscale is connected on your phone. If the connection fails away from home, check that first.
Guide
A short overview of how to install Tailscale on your server and your phone, so Seedly can reach your Transmission server away from home without opening any port.
Tailscale is a separate service from another company that links your own devices into a private network. Seedly does not need it, but it is a simple way to reach a home server from outside. This is only an overview: the Tailscale documentation has the details for every system.
Sign up at tailscale.com with an account you already have, such as a Google, Microsoft or Apple account. The free personal plan is enough for a home setup.
Install it on the machine where Transmission runs. On Linux a one-line installer from tailscale.com does it, and there are also packages for many NAS systems and for Docker. Then start it and sign in with your account, for example with the command sudo tailscale up.
Install the Tailscale app on your phone from the App Store or Google Play, sign in with the same account, and turn it on. Your phone and your server now see each other in the same private network.
In the Tailscale app or in its admin page, open the list of your devices and note the server’s address. It is a number that starts with 100, or a short device name that Tailscale can resolve for you.
Transmission only answers the addresses in its access list. Add the Tailscale range, for example 100.*.*.*, to the rpc-whitelist setting, or turn the list off, then restart Transmission.
In Seedly, open Settings, then Servers, and add a server with the Tailscale address as the host name. Keep the port (9091 unless you changed it) and the RPC path, and use Test connection before saving.
Seedly reaches the server only while Tailscale is connected on your phone. If the connection fails away from home, check that first.
You do not forward any port on your router. The traffic between your devices is encrypted by Tailscale, even if Seedly shows its warning for a plain HTTP address.
The same works for a search source. Use the Tailscale address of the machine that runs Prowlarr or Jackett.
Tailscale is a separate product and Seedly is not affiliated with it. Read its own documentation for the exact steps on your system.
The server settings guide explains what Transmission, qBittorrent and Deluge need before Seedly can connect.
Open the server settings guide