Hi Paulo,
Sorry if we accidentally misled you into thinking you would need a premium API key in the future. We had a patch available pretty quickly after your first message - see:
This patch (and the 3.1.5/3.2.0 releases) switch from API Documentation | Alpha Vantage to API Documentation | Alpha Vantage. This means we now only get the “daily open rate” instead of a near real time rate.
Having a premium API key doesn’t make any difference, but what we will do for the next 3.2 release is add a checkbox to the module config which says “I have a premium API key” and switches back to the current rate - see:
If you want the current market rate to be displayed, you can enable that option and continue using the premium key 
I hope that helps!