Seth stated in a radio interview....
“The promoters kind of hinted to me, and they gave me the money to stand and trade with him,” he told “The Monsters in Orlando” radio show. “They didn’t want me to take him down, let’s just put it that way. It was worth my while to try to stand up and punch with him.”
That would make it a fix, not a "bonus payout for a KO"
It could just mean they where offering a big bonus for a KO.
Which doesn't amount to a "fix", it just means they wanted a specific type of fight to happen. Which could be partly because stand up fights go better on camera, not to mention it was the only way Kimbo really had any chance, and he is there biggest headliner.