How to activate API which are to be considered for online payments in FICA

Hello guys,

We are doing an implementation project in SAP ISU and client gave us the requirement that they want to do online payments and it should be triggered directly in SAP so I found that it can be done API.IF

These are the API which are to be considered for online payment via FICA

API_CABUSPARTPAYMENT

API_CABUSPARTINVOICE

Please can anyone guide me how to activate the API and what other process need to be done to fulfill the requirement of our client

Or is their any other API which is missing or is their any other method which can be used to do the posting

Thanks in advance