Not able to get Instagram App Approval - Reviewer Http-Request Problems?

we are having a problem going through the review process of meta instagram review - our question is: Is there any settings in the reviewers browser or company network that prohibits sending data via XMLHttpRequest in our javascript code on our onboarding website (www.sensai-bot.de/fb-login)?

More detailed: We have a problem with the instagram review. when the reviewer performs the outlined steps at the bottom (reviewer sticks to the video explanation as expected) we send from our website (www.sensai-bot.de) the newly generated page access token for the linked page to our secured bot server.

This is done with the below outlined code "send_to_bot()".

We are receiving logs for all steps, including the click on the "activate bot" button and of the javascript code entering the function send_to_bot (as visible in the appended screenshot). However after this there are no further logs, our endpoint doesn't get triggered i.e. we do not receive the page access token from the reviewers page and thus cannot activate our app for the linked page. Therefore we get denied everytime.

This procedure works on multiple of our machines without fail.

steps:

1. reviewer is directed to our onboarding website frontend
2. reviewer clicks on Log In
3. a new browser window opens to link their page
4. reviewer chooses linked page for review purposes
5. reviewer clicks ok and proceed
6. reviewer clicks the button "activate bot" (see below screenshot 07:53:36.544 31.199s)
7. send_to_bot code gets triggered (see below screenshot 07:53:36.552 31.207s)
8. we expect our endpoint to receive the new page access token, however we don't receive a request at our endpoint consequently the onreadystatechange handler will not be triggered and we don't receive any further logs.

Logging Screenshot

function send_to_bot(page_access_token, user_id, app_id) {
Rollbar.info("send_to_bot start of function");
url = activation_url + "/onboard_page" + "?application_id=" + app_id + "&user_id=" + user_id + "&pat=" + page_access_token;
const Http = new XMLHttpRequest();
Http.open("GET", url);
Http.send();
Rollbar.info("send_to_bot: XMLHTTPRequest sent" + url);
Http.onreadystatechange = (e) => {
  dom_log_status(Http.responseText);
}

};

Below is my video screencast showing everything working perfectly:

https://www.youtube.com/watch?v=nQc6OyEOCbk&t=2s