Hi @cshinkin
In Braintree, they have a concept of merchant accounts. For each currency that you process payments in, you have a corresponding merchant account within Braintree.
If you navigate to the Braintree Settings > Advanced Settings > Merchant Account Settings page you can import those merchant accounts.
When creating a transaction, the Braintree plugin will find the merchant account that maps to the order’s currency and add that as a transaction property. That’s how Braintree’s API knows what currency you want to process the payment in.
Kind Regards