Scope + Account Permissions Info

Looks like you don't get the info necessary to embed the report, it could be a permissions problems on Power BI, try running
on the "Request builder test." form in this page admin/config/pwbi/api_test, this endpoint:

https://api.powerbi.com/v1.0/myorg/groups/[youe workspace]/reports/[your report]

It should return this data

{
"@odata.context": "",
"id": "",
"reportType": "",
"name": "",
"webUrl": "",
"embedUrl": "",
"isFromPbix": true,
"isOwnedByMe": true,
"datasetId": "",
"datasetWorkspaceId": "",
"users": [],
"subscriptions": []
}