VS402881: No artifact version is specified corresponding to artifact source 'MyBuild.' Release Management vNext REST API

Yes there are some disparities between the current version of VSTS APIs and the TFS 2015.2 APIs. But most of the APIs should work except a very few. Here is the documentation link.

Following is the required JSON for creating a release. The required JSON needs to have the name in instanceReference although its optional for the current version of VSTS API.

{
  "definitionId": 1,
  "description": "test",
  "artifacts": [
    {
      "alias": "Tailspin Toys",
      "instanceReference": {
        "id": "5",
        "name": "<build_name>"
      }
    }
  ]
}