Donations
All software in the Fediverse is developed by volunteers, and offered free of charge. If you enjoy using the software, please consider a donation to the developer. There are often links on the home pages for the software.
In addition to development, there are tens of thousands of 'Server Admins' who give up their time to run, administer, and support servers to run the software you use. There are regular costs associated with running servers. Again, consider a donation to your own Server Admin. Often they will have donation details in the About page for the server.
The donation amount can be a few dollars/euros/pounds. Every little helps with their costs.
Donations are generally not a requirement, but more of an 'if you can'.