LTI 1.3 - Getting 500 error from Token Service

Hi everyone,

We are working on LTI 1.3 implementation. We have deep-linking working and now trying to implement score service. However, we keep getting 500 (Internal Server Error) from the token service. We have followed steps outlined here 

OAuth2 Endpoints - Canvas LMS REST API Documentation.
 

We are generating a token request via a POST /login/oauth2/token with a grant_type of client_credentials and a properly formed JWT signed with our private key. The Scope is https://purl.imsglobal.org/spec/lti-ags/scope/score 

Here is a sample Score json.

{
"activityProgress": "Completed",
"gradingProgress": "FullyGraded",
"scoreGiven": 32.0,
"scoreMaximum": 100.0,
"timestamp": "\/Date(1572302484610)\/",
"userId": "bf14f352-16f3-498d-8f65-780b80b8c581"
}

We are able to get the tokens from other platforms. Is there anything we should be doing to get a valid token back?