Recently our users noticed INVALID_PROFIT_RATIO coming up for some of their bets. Betfair has changed how it processes bet orders and now bets with potential profit or loss less than £0.02 are not allowed and you see above error in such case. We’ve updated our code accordingly to fix placing of small bets, however if small stake is placed at low odds you still can see INVALID_PROFIT_RATIO error. For example, if your stake is £0.05 and price is 1.30, that means the potential profit is only £0.015 and such bet will not be accepted. So if you are betting in markets with low prices, like Horse Racing place markets, you should use at least £0.2 as a stake, so that even at 1.10 price the potential profit is valid on Betfair.