IEX v3 is a modul platform, meaning that the price consist of a subscription plan and a module (connector) for each system that is connected.
This structure is reflected in your invoice from IEX.
The subscription plan controls the subscription period, which functionalities are included and the usage limits for how much that can be transferred per month for the entire integration.
The modules are the connectors that are used to integrate to your systems. Each module has its own price, since they have difference operation and service costs. The price for the module is part of the IEX service and is not a payment to the system partner.
Extra shop domains that may have been added to your integration will be added as individual modules for the price of the system module.
Add-ons extends your integration with extra features. If mappings or hook-files are used on your integration the mapping module will be added to your subscription.