Schoology LTI 1.3 Deep Linking ltiResultLink processing failure

[amiroshn]

I am trying to integrate our application with Schoology. I am able to register app, initiate process of content selection, but when my app sends results back to Schoology, I get this:

{
  "error": "handleDeepLinkingLaunchInfo.error: fetch failed"
}

Here is decrypted payload of the token which my app posts to Schoology:

{
  "iss": "7503910734",
  "aud": "https://schoology.schoology.com",
  "iat": 1726784462,
  "exp": 1726784612,
  "https://purl.imsglobal.org/spec/lti/claim/message_type": "LtiDeepLinkingResponse",
  "https://purl.imsglobal.org/spec/lti/claim/version": "1.3.0",
  "https://purl.imsglobal.org/spec/lti/claim/deployment_id": "7503910734-1531251593",
  "nonce": "2d9293b0f3bf6",
  "https://purl.imsglobal.org/spec/lti-dl/claim/content_items": [
    {
      "type": "ltiResourceLink",
      "title": "Earth's Atmosphere",
      "url": "https://lti.qa.eb.com/lti13",
      "custom": {
        "link_url": "https://packs.qa.eb.com/science/208969#/pinboard"
      },
      "iframe": {
        "width": 100,
        "height": 100
      }
    }
  ],
  "https://purl.imsglobal.org/spec/lti-dl/claim/data": "a8c53ff5-3e5f-489b-a4e1-63b7154d6fcc"
}

What can be wrong with this thing?