Users are allotted 50 model runs per day for free. A model run is on a per map unit, per parcel, per scenario basis. If there was a single parcel with 5 soil map units and 2 scenarios (1 baseline, 1 future), then there would be 10 model runs used.
For example, if you have 1 field that has 11 scenarios (baseline + 10 scenarios) and 2 soil map units within that parcel, that would be a total of 22 model runs and would be within the daily free limit.
If you are interested in running additional daily API runs, we can connect you to the right folks to set you up with more substantial model run capability for a fee.