SOOS accounts start with 5 contributing developer seats.   The number of seats selected at purchase should reflect the number of contributing developers on your team.  The maximum number of contributing developers you have performing scans using SOOS should not exceed the number of purchased seats. 

Paid Standard Edition accounts can increase their seat count in increments of 5 by moving the slider found on the Billing page and proceeding to checkout to update their subscription plan selection.  Note:  Subscriptions of 30+ seats will be billed yearly.

SOOS billing page, adding contributing developer seats