It's also possible to download the accounts.json file and transfer it into the directory. By the looks of it on MacOS the directory is $HOME/Library/Application Support/PrismLauncher/.
Edit: If you are using the portable Windows version you can place the accounts.json file in the root directory of the install.
I have tried many times to use it and it didn't work either on windows or on linux, indeed the one I have on github changed 2 times from the one you currently are commenting