post {protocol}://api.ws.sonos.com/control/api/{version}/sessions//playbackSession/seekRelative
Use the seekRelative command in the playbackSession namespace to seek to the a relative position in the track with the specified cloud queue itemId.
Use itemId to ensure the group seeks on the current item. If the current item’s itemId does not match the one provided, the player returns ERROR_INVALID_OBJECT_ID.