I am able to receive and authenticate ContentItemSelectionRequest requests from Moodle.
I am constructing a response which I believe matches the LTI spec for a ContentItemSelection. I am signing it with oauth and sending it to the url that is given in the request, in my case:
However, I get a 404 response from Moodle, with an html body that says:
Incorrect sesskey submitted, form not accepted!
This is surprising... since I am submitting the sesskey right there in the url. I am at a loss of how to debug this further... I've seen some users having issues with sesskey elsewhere, but I don't know enough about Moodle itself to really be able to dig further.
Is this an issue with what I am sending to Moodle? Or is it something about my Moodle session setup?