I'm seeing some strange behaviour with the API. I place a bet through the API and then I immediately modify it to KEEP. The next time I get the unmatched bets on the market, the bet I just modified (sometimes) retains the AtInPlay state = CANCEL. The Bet Angel GUI correctly shows the bet as KEEP.
The steps I take are:
1) Get the available markets from BetFair
2) For each of those, add it to Guardian
3) Get all bets on the market
4) Check if there is already a bet so I don't place it again
5) If there is an unmatched bet with state Cancel, I change it to KEEP. <== This seems to happen on bets that is already KEEP, but not all.
6) Place bets if not found
7) Change bet to KEEP
8) Rinse and repeat some minutes later.
But all in all I like the API. It has postponed my investment in a Betfair key for now
Cheers