When adding a new enabled user or enabling/disabling an existing user in RPM a message will be displayed with a confirmation that the enablement/disablement of the user will affect your current billing cycle.
When enabling a user (agency, customer, or staff) a message will appear that the enabled user will immediately affect the subscription's latest billing cycle.
Ensure that you check the confirmation checkbox before adding the user.
When disabling a user (agency, customer, or staff) a message will appear that the disabled user will drop off the next billing cycle for the subscription. This is different than the enabling of users which will immediately affect the current billing cycle as RPM post bills and any disabled users will still appear on the latest invoice they were enabled for.
Ensure that you check the confirmation checkbox before disabling the user.