How to enter a client payment made on a third party platform that charges a fee. The platform is not a credit card, it is my scheduling platform?

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The client is invoiced for the full amount of our service.  She pays for the service on our scheduling platform.  The platform pays us the invoiced amount minus a fee. How do I credit the client the full amount, while having the cash reflect the amount minus the fee.

I understand the transaction but do not know how to create the entry in Sage.