Why am I receiving the INVALID_PROFIT_RATIO error?

This error is to prevent minimum bet rounding abuse (for certain stakes and amounts)

This doesn’t impact all bets below £2 but only those that meet specific criteria which we consider unfair.  

Any attempt to place, cancel or update a bet at these stake and price combinations will result in the error INVALID_PROFIT_RATIO

This is in-line with our terms and conditions that state the following:

Taking advantage of rounding off
You are not permitted to place bets or try to place bets which deliberately take advantage of Betfair rounding off to the nearest penny or cent. Any bets which seek to do so will be automatically cancelled.

Please see an example below:

An attempt to place a bet (including a bet used a size-up edit or price change) or cancel a bet down to a remaining size, such that it returns 20% less or 25% more [1] than it ‘ought’ to, that bet will fail with an INVALID_PROFIT_RATIO error returned to API customers – (customers attempting such on the Betfair website or mobile app will receive a generic error).

For example – a 13p @ 1.06 back bet is ‘unfair’ as it ‘ought’ to win 0.78p, but actually - due to rounding - wins 1p, a 28% uplift.

So attempting to:

• Increase the size of a £2.00 bet @ 1.06 to £2.13 (which creates a new 13p bet @ 1.06)
• Cancel £1.83 of a £2.00 bet @ 1.06 (to leave a 13p remainder @ 1.06)
• Price-editing a 13p @ 1000 bet to 13p @ 1.06 (which cancels the bet @ 1000 and creates a new one @ 1.06)

Will all fail with the error above.