One account can own several servers, so a login that only identified the account would leave the SFTP daemon with an unanswered question the moment it tried to open a file: which server's files, exactly?
Why it happens
A regular panel login authenticates you as an account. SFTP needs more than that — it needs to know which specific server's filesystem you are asking to browse, because the daemon is serving many containers from many accounts at once. The generated username solves that by combining both pieces of information into one string: your account name, a dot, and the unique identifier of the specific server container — functioning less like a personal login and more like a per-server one that happens to also prove who you are.
What to do
- Open the SFTP Details tab on the specific server
Not the account's general settings — the exact username shown there is scoped to that one server.
- Copy it exactly, dot included
It is not your billing email and not your display name; typing it from memory is the most common way this fails.
- Use the panel password, same as login
No separate SFTP password exists to look up.
The SFTP client authenticates and shows that server's file tree — not a permission error, and not somebody else's server.