After clicking to launch a TestOut LMS integration link in your class page or school portal (Canvas, Blackboard, D2L, etc.), instead of being taken to the module, you are taken to the labsimapp.testout.com login page. This is known to occur in Firefox and Brave browser.
Note: An alternate symptom of this problem is the "We had trouble preparing your TestOut experience (Third-party cookies)" error. The solution below will generally fix both problems for Firefox users.
On the school portal page you were on where you clicked the link to launch TestOut, click the shield icon in Firefox's address bar to the left of the URL. Toggle off the Enhanced Tracking Protection setting, then try clicking your link to launch a TestOut module again.
This should take you right in, bypassing the login page. If you still experience the problem, try it in another browser (Chrome, Edge, or Safari).
If using Brave browser, switch to another browser.