Only locked plans can be used by APIs in the organization. So, if you have configured all policies you want to use in a plan, you will have to lock it, before it is ready for use. Locking a plan is simple and can be done from any tab of the plan details page - just click the Lock Plan button in the basic settings of the plan in question:
Locking the plan will prevent all future policy changes, and make the plan available for use by APIs. The new status of the plan 
Make sure that the configuration of the plan is finished before you lock. Locked plans cannot be revised. To change an already locked plan, you need to create a new version of the plan (see Versioning).