When you are having troubles with the API, I would take the time to inspect your network traffic when performing the desired action in the Orchestrator Web UI or Swagger for comparison.
When I performed an upload in Cloud, the following endpoint was used
When performing the action via Swagger, it is successful and also generates the following curl command
curl -X POST "https://cloud.uipath.com/<account_name>/<tenant_name>/orchestrator_/odata/Processes/UiPath.Server.Configuration.OData.UploadPackage" \
-H "accept: application/json" \
-H "Content-Type: multipart/form-data" \
Could you provide more information about your Request Payload and headers along with the response code & body?
Along with inspecting your requests, here are some helpful references
Another resource that I review from time to time is the UiPath Orchestrator PowerShell Module’s source code. UiPath.Powershell