Creates an upsell for a project.
| project_id required | integer Project ID. You can find this parameter in your Publisher Account next to the name of the project.  Example:  44056 | 
Upsell has been created for the project.
Authentication not passed or wrong.
Item not found.
Invalid request.
{- "is_enabled": true,
- "type": "fixed_list",
- "items": [- "game_sku_1",
- "game_sku_2",
- "game_sku_3"
 ]
}{- "statusCode": 401,
- "errorCode": 1501,
- "errorMessage": "[0401-1501]: Authorization failed: Provide authorization"
}