This sounds like the problem I reported a while back here:
https://forum.bitsquare.io/t/payout-transaction-not-working-as-described/587
Please note, I used the phrase ‘What appears to be happening…’. If this is working as designed then it’s lame (IMHO), if not, then it’s a bug obviously.
In my case, the peer was online for the whole time that I was waiting for the transaction to finalise. I know that because I’d tagged him, and he had other open offers available the whole time.
I had exactly the same error message as BlueCustard here i.e. ‘Wait until peer finalizes the payout transaction’.
I gather from the arbitration that followed (no other option), that the buyer was similarly waiting!
It shouldn’t be necessary to send messages outside of the system to confirm what should be happening automatically as I emphasised in the other thread. The seller confirming he has received the funds should be the trigger that ends the transaction whether the buyer is online or not (again IMHO).
Whether the buyer is online or not is irrelevant. If I make a fiat payment to someone’s bank, the payment still exists whether they acknowledge it or not.
HTH?