Associates one or more existing products with the task so they show up in its product scope; products already associated with the task are silently skipped rather than causing an error. Fails entirely, with no partial assignment, if any requested product id does not exist in the organization's product catalog. To remove a product from the task instead, use DELETE /tasks/{taskId}/products/{productId}; to mark a product done or not done within the task without removing it, use the complete/revoke endpoints.