: The key is typically sent via email as a file named yourname.cyberducklicense .
You can contribute any amount, though there are suggested minimums to receive a license key. Cyberduck Registration Key
Once you receive your .cyberducklicense file via email, follow these steps to apply it: : The key is typically sent via email
David V. Kocher, the lead developer, has publicly stated multiple times on the Cyberduck mailing list and GitHub issues: the lead developer
Because Cyberduck is open-source, you never have to pay. But should you?
Cyberduck is open-source software distributed under the GPL license. This means it is technically free to download and use. However, the developers use a "donationware" model to fund ongoing updates and maintenance.