"var access_token = $J("[data-loyaltystore]").data("loyaltystore").webapi_token;
var badgeid = 0;

SetFavoriteFeaturedBadge(access_token, badgeid);

function SetFavoriteFeaturedBadge(access_token, badgeid) {
$J.post( 'https://steamproxy.net/steamapi/IPlayerService/SetFavoriteBadge/v1?', {
access_token: access_token,
badgeid: badgeid
});
}

links to the other stuff in case it didn't work this way:

https://steamproxy.net/discussions/forum/1/2577697791645081164/#c6756004301607388784

https://steamproxy.net/sharedfiles/filedetails/?id=2947375220"