I'm not familiar with betcoin's live betting since i've only tried them pre live but if the score changes while you're betting there should be a notification about an odds change asking you to confirm the bet for the second time.

On the other hand it could be just some bad timing since there's a delay. I also experienced this with other sportsbook when I was live betting some tennis match before I could lock my bet the odds kept getting smaller and at the same time my bet gets rejected.