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Test 8.1 for LTI v1.2

Test 8.1 for LTI v1.2

I can't get test 8.1 to be marked as passing even though everything seems to be working fine. Upon launching, my platform requests the Tool Consumer profile and IMS responds with a valid TC profile. The user is then redirect to the platform. Upon ending the session, the user is redirected back to the return URL specified by the launch request. From my understanding, everything that was necessary was done. Is there anything I might be missing?