Marks a saved card as the default. The previous default card is automatically unset.
The default card is the one pre-selected when the user chooses saved_card as
payment method on POST /escrow-fund.
JWT access token obtained from /auth-verify (login context) or /auth-signup. Set the bearer_token environment variable in your API client to apply it globally.
"c1d2e3f4-a5b6-7890-abcd-ef1234567890"
Default card updated