Using REST API with JSONP and pretty permalinks disabled

I am using the WP REST API with WPv4.8 with pretty permalinks disabled (security reasons). I can successfully do a GET request to the posts object like so:

https://url/blogs/usernamehere/?rest_route=/wp/v2/posts

And, I can do a successful JSONP callback with pretty permalinks enabled. However, when pretty permalinks are disabled, I can not do a successful GET request with JSONP. I get a 404 NOT FOUND when using JSONP callback like so:

My callback function:

jsonp.js file:

var posts;
function receiveData(data){
posts = data;
}

My HTML index file:

<script src="jsonp.js></script>
<script src="https://url/blogs/usernamehere/?rest_route=/wp/v2/posts?_jsonp=receiveData"></script>

Has anyone tested using JSONP with pretty permalinks disabled? Any clues on what I am doing wrong ? Thank you

[Moderator note: First URL corrected per OP’s second post. Second post archived so OP remains on no replies view.]