Flag and Rules for notifying content changes

I am trying to use Flag and Rules to send an email when group content changes.

{ "rules_og_new_content" : {
"LABEL" : "OG new content notification",
"PLUGIN" : "reaction rule",
"OWNER" : "rules",
"REQUIRES" : [ "og", "flag", "rules" ],
"ON" : { "node_insert" : [] },
"IF" : [ { "og_entity_is_group_content" : { "entity" : [ "node" ] } } ],
"DO" : [
{ "flag_fetch_users_node" : {
"USING" : { "flag" : "groepnotificatie", "node" : [ "node" ] },
"PROVIDE" : { "users" : { "users" : "Users who flagged" } }
}
},
{ "LOOP" : {
"USING" : { "list" : [ "users" ] },
"ITEM" : { "list_item" : "Current list item" },
"DO" : [
{ "mail" : {
"to" : [ "list-item:mail" ],
"subject" : "New post in group",
"message" : "Hello [list-item:name],rnrnThere is a new post called [node:title] that belongs to one of the groups you are subscribed to.rnrn[site:name]rn",
"from" : [ "" ]
}
}
]
}
}
]
}
}

However, the users list is empty. Anyone have any ideas?

Drupal version: 


Source: https://www.drupal.org/taxonomy/term/22/feed