not a lightning guru, yet the message say it clear: unknown error means it is not documented? apparently the channel has not enough inbound liquidity, or there's not a suitable route to deliver the payout. if it keeps failing, an alternative is to accumulate earnings until they reach the on-chain threshold, at which point they are paid on-chain to your Bitcoin address as a fallback if you have set one.

best you can do is to contact ocean, as suggested.