Route In/Out/In/Return

Hi,
We have a content testing platform that we need to integrate with Qualtrics.
The typical flow of an event is:
Attendee is checked in
We route them to Decipher with some variable on the URL string
Decipher uses those variables to make a RESTful API call back to our platform
Decipher parses the JSON response and populates the associated questions in the Pre-Stimuli portion of the survey
Decipher then prompts the respondent with the remaining Pre-Stimuli questions
Decipher "suspends the survey" and routes the respondent back to our platform with some of the originally sent in variables and a token that represents the place within the survey the associated respondent is in.
The respondent participates in the event / watches the content / provides their feedback
After the stimuli, we redirect them back to Decipher with that token we were sent and a couple of additional variables.
The respondent finishes the post-stimuli questionnaire
Decipher then [using the Return Links] redirects them back to our platform along with some of the variables we sent in when they returned to Decipher for the 2nd time.
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That is how it works in Decipher. I need to figure out how I can accomplish the same thing without changing the way that our platform works.
Does anyone know how I'd simply achieve the following:
Platform X generates a URL like this and redirects the respondent to Qualtrics:
https://survey.qualtrics.com/jfe/form/SV_9p1ylT5ZBpboBka?encryptedsessionid=adfsadsf&id=12341234&jwt=asfdasdfadsfadsf&prerequestid=asfdasdfasdf
Qualtrics generates a link like this and redirects back to Platform X:
http://www.platformX.com/adfsadsf/asfdasdfasdf?id=12341234&state=R_1K6G8HqpGYMRT5E
Then, when Platform X returns the respondent after the stimuli is shown, we need for them to pick up where they left off.
https://survey.qualtrics.com/jfe/form/SV_9p1ylT5ZBpboBka?state=R_1K6G8HqpGYMRT5E

NOTE: I have achieved the first part of reading the values into Embedded Data.
Then, on the last question of the Pre-Stimuli I am using Display Text and the JavaScript

Qualtrics.SurveyEngine.addOnload(function()
{
/*Place your JavaScript here to run when the page loads*/

var encryptedsessionid = "${e://Field/encryptedsessionid}"
var id = "${e://Field/id}"
var jwt = "${e://Field/jwt}"
var prerequestid = "${e://Field/prerequestid}"
var state = "${e://Field/ResponseID}"

window.location.href = 'http://www.example.com/session/' + encryptedsessionid + '/' + prerequestid + '?id=' + id + '&state=' + state
});

One of the issues is that, when they return is, they return to that same page and are immediately redirected again. I need for them to be returning to the next page / not the same page they left off on.
Any help solving this would be great!
Jason