Upsert your Collection Products. This endpoint is combination of bulk update and bulk create. Colection identifier is "Collection Name". Product identifier is "product_external_id" (with addion of optional "product_identifier"). If a product already exists in Collection, it will be updated. If a Product does not exists in Collection, it will be added. This endpoint is async, so you will receive a job_id which you can use to check a status. Default limit of objects which can be sent within single request is 20. Limit is total number of Products, not Collections (eg, you can send 2 Collections each having 10 Products)