My school uses D2L Brightspace. We believe we have basic LTI Advantage functionality working now (single-sign-on, WW account creation, automatically assigning the right things to a new WW account).
I've moved on to testing grade passback, starting with "course" mode. When there is an attempt to send grades back, it fails, and the log has entries like:
[2023-08-17 17:52:52.07412]  [warn] [LkfLuGs9SrkR] [/webwork2/new-lti-1p3-test/Orientation/5] Submitting all grades for user ww12345
[2023-08-17 17:52:52.34008]  [warn] [LkfLuGs9SrkR] [/webwork2/new-lti-1p3-test/Orientation/5] Failed to obtain access token from LMS:
Is anyone using D2L with WeBWorK, with LTI 1.3, with grade passback and having success? Or has insights that might help us?