Does the GPL allow me to charge a fee for downloading the
program from my distribution site? (#DoesTheGPLAllowDownloadFee)
Yes. You can charge any fee you wish for distributing a copy of the program.
If you distribute binaries by download, you must provide “equivalent access”
to download the source—therefore, the fee to download source may not be
greater than the fee to download the binary.
https://www.gnu.org/licenses/gpl-faq.html#DoesTheGPLAllowDownloadFee
GPL3 source code is here: https://gitlab.com/mardy/photokinesis.git
...the GPL gives them the freedom to release it to the public, with
or without a fee. For example, someone could pay your fee, and
then put her copy on a web site for the general public.
…
You can charge people a fee to get a copy from you. You can't require
people to pay you when they get a copy from someone else.