How much work is it to build an Integration for Protect Content Plugin?

I know these things are difficult to predict, but can any of you "Coders" give me an idea on how much work it is to integrate "Protect Content" with a Marketplace? An integration with the german Marketplace "Digistore24" (something like Clickbank or ShareIt, but german) would be very useful to me.

One thing I know is that Digistore24 offers a very good API (if you want download here some PHP classes https://www.digistore24.com/download/package/digistore-api.zip and see the API references https://doc.digistore24.com/technik/api/api-referenz/ ).

Any first estimation on how much work it would be for a good Coder to build such an integration?

I would appreciate it, Thank you!