I don't work with Inquisit. But I can see that URL doesn't contain a query string to identify the subjectID. In order to capture that info, the URL itself will need to contain the info:
mili2nd.co/4n7b?subjectID=123456
You'll need to alter the URL being sent so that it contains that identifier for Qualtrics to capture it.

Hi Kate,
Thank you for getting to my inquiry. Does that mean I have to create new query strings for each participant? I’m trying to have 200 participants complete the survey

In order to capture unique SubjectIDs, yes.
If you have the participants pre-identified, upload them with SubjectID as a embedded data category. If you're using qualtrics mailer or mail merge to distribute, simply pipe that ID into the URL. That makes it so you're not hand-creating 200 unique IDs.