*NOTE: additional user invites are only for paying customers, in other words, you can't add additional users unless you stop the free trial and upgrade to a premium account.
a. Go to "Manage Users" in account dropdown
b. Click on Upgrade Account
c. Click on Ad Ons
d. No click on "+" or edit the "Additional Agent" field to the amount of agents you wish to include and then click on "Confirm Change"
*Now that you have purchased invitations, you can go-ahead and send invites to additional users.