How does cashout affect the bets we send to you?

E.g., if we have a multibet where only one leg gets cashed out, but other legs are settled in the end of corresponding events (including, for example, foreign events), will there be any problems with processing in OTS?

We do not consider which selection has cashout. You just need to send the total cashout amount in the cashout_stake parameter within the TicketCashout fields, and as long as the cashout amount is not higher than the max possible payout, it will be accepted.