The DHIS2 Developer documentation discusses here, the ability to POST multiple events to the Web API in a single payload, which is absolutely useful. Is this feature also available for updating existing events via a PUT request, In DHIS2 2.27 and later?
No, this is not possible (with PUT). What you can do, is to just do a POST, but set strategy=CREATE_AND_UPDATE and that should give you what you want (strategy=UPDATE if you are sure its all updates only)