channelId
channelId: `ch_${string}` = ...
fromId
fromId: `ak_${string}` = ...
offChainTrees
offChainTrees: `ss_${string}` = ...
payload
payload: `tx_${string}` = ...
round
round: number = shortUInt
stateHash
stateHash: `st_${string}` = ...
update
update: `cb_${string}` = ...