up-bank-api has to retrieve the full transaction list before it is available.

unpaginate returns an m [[a]] where m is often the ClientM monad from Servant.Client.Internal.HttpClient

This can be interpreted as returning a list of "chunks" which can later be concatenated to form the whole result. An incorrect assumption was made that this IO lists are lazy.

Use a streaming library.

https://stackoverflow.com/questions/32489732/lazy-list-wrapped-in-io
https://stackoverflow.com/questions/5892653/whats-so-bad-about-lazy-i-o
https://stackoverflow.com/questions/7191058/truly-lazy-io-in-haskell
https://stackoverflow.com/questions/32151151/haskell-api-client-pagination