REST API: Update Report Content Error "PowerBIEntityNotFound"

Hello fellow Data Nuts 😁

I decided to dip my toe in the mystical world of the PowerBI REST API today and while I am up and running I am facing an issue where I am getting an error when I am trying to use the "Update Report Content" API Call.

{
"error": {
"code": "PowerBIEntityNotFound",
"pbi.error": {
"code": "PowerBIEntityNotFound",
"parameters": {},
"details": [],
"exceptionCulprit": 1
}
}
}

POST https://api.powerbi.com/v1.0/myorg/groups/{groupId}/reports/{reportId}/UpdateReportContent

{ 
"sourceReport": { 
"sourceReportId": "{sourceReportId}", 
"sourceWorkspaceId": "{sourceWorkspaceId}" 
}, 
"sourceType": "ExistingReport" 
}

I have a valid bearer token, and other API calls are working fine. I am copying the group and report guid's direct from the URL's in the service but still getting the error message above.

Also, i do have the app setup correctly with all azure app settings, definitely has the correct scope for the call.

Hoping somebody could help me troubleshoot this api call.

Thanks in advance,

David