If you use more than 1GB per 1 month, you will be automatically charged $8 (€7.50) and 1GB of data will be added to your GoFi line when your data falls below 100MB.
Once you've used 8GB in a month, your data charge is capped at $64 for the rest of the month, but you continue to get full-speed data service. Slow down after 30GB.
At the beginning of the next month, your data consumption is nulled and you will be automatically charged $8 (€7.50) for 1GB of data per month. This is done to ensure that your service is uninterrupted.