Your link does not work.
This works for me though:
GET /post_action_users?id=13&post_action_type_id=2
This outputs
{
"post_action_users": [
{
"id": 1,
"username": "ausername",
"name": null,
"avatar_template": "/letter_avatar_proxy/v2/letter/i/{size}.png",
"post_url": null,
"username_lower": "ausername"
},
{
"id": 10,
"username": "anotherusername",
"name": null,
"avatar_template": "/letter_avatar_proxy/v2/letter/{size}.png",
"post_url": null,
"username_lower": "anotherusername"
}
]
}
Which is a list of users who liked the post with id 13