The back-end

A super simple UML design for your database potentially looks like this:

Database tables (UML)

In the example above: an end-user would give you access to multiple financial assets by completing onboarding session/s. Each asset has a pointer to the respective Finqware resource in the form of the pair [finq_credentials_id, finq_access_token]. It also has a number of transactions associated - if the asset is for example a credit card.