To implement cross-HTTP request optimistic locking, each event object sent from the server has a version stamp assigned to it. When updating an event, be sure to load the event data from the server, provide updates, and send the updated event data back to the server with the same version stamp that was sent in the original server's response.
For example, if the server sends event data with version stamp 12345, you must send back the updated event data with version stamp 12345. If these versions don't match, it means that the data has been edited by another client, and the server throws an error.