What if they never answer?
On a paid inbox, every euro returns to you automatically when the window closes. On a free inbox your track waits in their queue, and you see the moment it is played.
Who can hear my track?
Only Brawther and anybody they share their workspace with. It is never listed, never public, and never shown to other senders.
Can I swap the file after sending?
Yes, until they open it. After that the version they heard is the one on record.
Can I send the same track twice?
Not while it is still waiting in that inbox. Once it has been opened you can send a new version.