dynamic registration suddenly getting 422 "Unprocessable Entity"

[JosiahHooten]

I am attempting to make a dynamic registration process for an LTI tool so that it can be added to Canvas. I had it working but I'm now getting "Unprocessable Entity" when I post to the canvas-specified endpoint with the provided token. The register body is as follows (slightly redacted). Any suggestions? Could it be a problem in the Canvas installation?

{
  "application_type": "web",
  "response_types": [
    "id_token"
  ],
  "grant_types": [
    "client_credentials",
    "implicit"
  ],
  "initiate_login_uri": "https://tool.client.org/lti/login",
  "redirect_uris": [
    "https://tool.client.org/lti/login",
    "https://my.client.org/lti/login"
  ],
  "client_name": "client.org",
  "jwks_uri": "https://tool.client.org/lti/jwks",
  "token_endpoint_auth_method": "private_key_jwt",
  "contacts": [
    "admin@client.org"
  ],
  "scope": "https://purl.imsglobal.org/spec/lti-ags/scope/lineitem https://purl.imsglobal.org/spec/lti-nrps/scope/contextmembership.readonly",
  "https://purl.imsglobal.org/spec/lti-tool-configuration": {
    "domain": "https://client.org",
    "description": "client.org LTI Integration",
    "target_link_uri": "https://tool.client.org/lti",
    "custom_parameters": {
      "email": "$Person.email.primary",
      "full_name": "$Person.name.full",
      "given_name": "$Person.name.given",
      "family_name": "$Person.name.family",
      "display_name": "$Person.name.display",
      "section_ids": "$Canvas.course.sectionIds",
      "section_names": "$com.instructure.User.sectionNames"
    },
    "claims": [
      "sub",
      "iss",
      "name",
      "given_name",
      "family_name",
      "nickname",
      "picture",
      "email",
      "locale"
    ],
    "messages": [
      {
        "type": "LtiResourceLinkRequest",
        "label": "Launch client.org",
        "placements": [
          "link_selection"
        ],
        "icon_uri": "https://www.client.org/assets/favicons/client-favicon.ico"
      },
      {
        "type": "LtiResourceLinkRequest",
        "label": "Launch client.org",
        "placements": [
          "assignment_selection"
        ],
        "icon_uri": "https://www.client.org/assets/favicons/client-favicon.ico"
      }
    ]
  }
}

.  

[pwhitmer8]

Our tool suddenly stopped working for dynamic registration, for 2 customers trying to install us in Canvas. So we had to walk them through a manual flow. Not great!

Was there some notice that we missed? We didn't change anything on our side.