Bookmaker BetVictor eventually paid out a £625 bet after a dispute with a punter over whether the ball hit the woodwork during a match.
Celtic fan David Reid put £5 on a 125/1 special in the Barcelona v Paris St Germain Champions League match on Wednesday.
He correctly predicted Barca would qualify, Lionel Messi would score a penalty and that Edinson Cavani would hit the woodwork.
BetVictor initially refused to pay out, arguing that the ball must come back into play after hitting the woodwork to count.
Mr Reid vented his anger on Twitter and, after support from other users on social media, BetVictor eventually relented.
The company apologised and Mr Reid said he had been given a £20 free bet.
BetVictor have also changed the terms of the 'hitting the woodwork' bet.
In a statement, BetVictor said: We accepted a small number of bets on a #PriceItUp market, ‘Messi to score a penalty, Cavani to hit the woodwork and Barca to qualify’ at 125/1 in the Barcelona v PSG Champions League match.
"Customers request this type of tailored bet via Twitter and our Trading and Social Media teams price up the requests and reply to customers.
"We settled these particular bets as losers, as under our betting rules for #PriceItUp, which are listed on our website, we have the following rule regarding woodwork-related bets.
‘’For any bets involving players hitting the woodwork, the following rule will be applied: The ball must make contact with the woodwork and come back in play from an attempt on the opponent’s goal during active play. Shots that hit the woodwork on their way into the goal will count.
"As Cavani’s shot against the woodwork didn’t rebound back into play, we settled these bets in line with the above rule, which was designed to prevent ambiguity around shots that may or may not have skimmed the woodwork.
"However, we accept that in this case with #PriceItUp markets, these terms were not made clear within the individual bet, and, as such, have now settled all bets on this selection as winners. All of the customers involved have been individually contacted by us.
"Moving forward, to avoid any confusion, we will update the relevant rule and publish it ahead of our next #PriceItUp fixture, which is scheduled to be next Monday 13th March for the FA Cup 6th Round clash between Chelsea and Manchester United.
"We can confirm that any shot that hits any part of the woodwork will count going forward.
"We apologise for any confusion caused."