In order to use the syndication fork in your flarum instance at the time of writing this:
There is no version tags yet, so edit your composer.json and in the "require" section, use "dev-master" instead, e.g.:
"amaurycarrade/flarum-ext-syndication": "dev-master",
And because it is not in packagist currently, you need to add the git repository to override the packagist one just for it. This won't affect other dependencies which will continue using packagist:
"repositories": [{
"type": "vcs",
"url": "https://github.com/GuDzpoz/flarum-ext-syndication"
}],
