At the current code-base (right side) there is no "setAccept" method called, so the request sends without any "accept" header which cause an error on the our backend and the LTI Grade Service doesn't work because our server can't accept the request without "accept" header.

File lib/lti1p3/src/LtiServiceConnector.php:68-78

Adding the following code resolves the issue.

$request->setAccept('application/json'); 

Could you please fix this or is it irrelevant?