New "tax_rate" and "tax_country" fields on DIVNRA activities

Broker API

Adds tax_rate and tax_country to the DIVNRA activity schema, exposing the tax country and withholding rate applied when the activity was booked.

Affected Endpoints

• GET /v2beta1/accounts/{account_id}/events/activities/{event_id}
• GET /v2beta1/events/activities