Sandbox apps

If you use Teams, you may develop apps using Sandbox-plan (it is included into each developer seat). The plan (in terms of features) is identical to Pro plan.
As soon as you ready to launch app to production (deliver it to the client), upgrade the team plan, but keep it within the team — you'll get the affiliate reward then!

How to use Sandbox plan

Option 1. Create app with Sandbox plan from the Team page

Option 2. Creating/updating an app from the home page