question

First of all the platform sandbox is free of charge. You pay fees only when you are doing actual business .

Then the business model depends on various aspect , Like Finastra is that a reseller agreement , or a referral agreement

there are a dedicated video on the documentation carrousel
here https://developer.fusionfabric.cloud/documentation

look at the video titled : "Partner on boarding & commercial" and to the one called "Platform commercial model"

you have also information there

https://developer.fusionfabric.cloud/documentation/program-guide/program-guide-commercial

short story : if it is a referral model Finastra is applying a 20 % revenues fees till 250k of booking .