Yeah, I don't know what happened to the player, but I guess he just accepted the defeat cause its 4-0 3rd set, and I also have to accept that I can't win this bet. lol I've already accepted the final decision by sportsbets.io on this bet. Steve already PMed me and discuss about how void bets on tennis works and I fully understand it now. Steve gave me another free bet since he think that I'm active on posting in this thread, also if the freebet is voided, it's not refundable its like consider as lost.
I'm fine with this now, at least I was given another freebet by Sportsbet.io/Steve and thanks to them, I got another one.
I'll now avoid betting my free bet on tennis. I learned a lot from this experience. Lol.
I doubt he "accepted his defeat" and that's why he retired. That's actually against the rules. If you are fit to play you must show your best trying to win. If they give you a "lack of effort" penalty you can lose ranking points, price money and so on. This happened in the past and the player in question then had accusations of fixing games.
So every retirement is basically due to medical reasons. It's a common practice for sports books to void bets like this. Only bets where no other result is possible mostly get graded. Mostly that's like under/over bets where no other result than over is possible, even if the over is not reached yet, and so on.
Some books have/had a rule that there is no void after the first set is completed, but that's quite rare. Maybe next time your player is losing and retires and you get your money back. It all evens out in the long run.