Double Entry Accounting Features Development

I know there is an app from akaunting.com for double entry (https://akaunting.com/apps/double-entry)

But, I need some answers for my case:

1. If I bought the double entry app, can I have access the code or API docs of double entry? Because in my case, I need to develop accounting for Indonesian non profit organizations and I need to use the API for the architecture because I need to create new API that will fit to user.
2. Or, Can I just using the base code of the akaunting.com free version then I develop by myself to make double entry features? Right now, honestly I still doubt if I can develop by myself to make double entry features based on akaunting free version, because the docs is not that good for API, or am I missing something?

NB: I have installed and tried some features at versions of akaunting.com, I installed version 1.13 until 2.1.0 .

Thank you,
Regards,
Luthfi Abdurrahim

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