I haven't used the Caliper API in production before, but if you have access to the SDK, you can deploy an extension as a custom endpoint and then query the DB as needed for transactions.

Here's a decent writeup for Transactions in the SDK docs: https://docs.q2developer.com/guides/database/transactions.html

When I needed to pull transaction data, I had an extension that queried the Backoffice API - Generated Transactions endpoint (via the DB object in my SDK extension). It was a periodic job that ran every night and pulled an entire days worth of Generated Transactions (trans that originated in the Q2 system, not the core) and analyzed them for certain properties. However, to instantiate the DB object, I needed to pass in HQ credentials which needed to be setup by another employee at my FI. Then they needed to be rotated every so often.

Backoffice API docs: https://docs.q2developer.com/guides/online_integration/backoffice_calls.html
Generated Transactions docs: https://docs.q2developer.com/api_references/q2_sdk/db/db_objects/generated_transactions.html#module-q2_sdk.hq.db.generated_transactions

Hopefully something here is helpful!