First thing first, just to make it clear.
The error you are seeing
errorCode":"error.public-api.exceeded-api-key-allowance"
Means that there has been too many calls in a too short time period. So your historical quota has not been consumed, when that happens the message is slightly different.

If you open the logback.xml (same directory as plugin log file) and change log level from info to debug for only for this line
<root level="info">

You should get some more info on exactly what data zorro is asking for.

Have you also made sure that you are indeed using the same assets for the IG plugin and FXCM? Could you please post your assets file for both?
The +1 vs +205 has nothing to do with the plugin as far as I know.