Websocket client ItemCommandEvent with issues

Does anyone know what I’m doing wrong in my request? I tried the following command, but there must be something wrong in the json, as I always get an error back. The item does exist in the registry.

Failed to process deserialized event '{"eventId":1,"payload":"{\"value\":\"OFF\"}","source":"WebSocketTestInstance","topic":"openhab/items/MY_ITEM/command","type":"ItemCommandEvent"}': Error parsing simpleClassName 'nullType' with value 'OFF'.

The solution is to add the type to the payload object.