We send a cashout request to you and you reject it. How should we handle it?

I see that, if the bet request itself gets rejected by you but we would decide to accept it, we should send ticket acknowledgement – should it be the same with cashout?

A cashout request will never be rejected arbitrarily, only if there is an error on your side with sending it to us (according to the list of possible errors in the OTS doc - TicketCashoutRejectReason codes). If the cashout is sent correctly, we won't reject it.