Set an end-user's credit balance to a specific target amount. Useful for synchronising balances, applying refunds, or correcting discrepancies.

The API calculates the delta automatically (delta = target_balance - current_balance) and applies a single positive or negative adjustment.

Idempotency: Each reference_id can only be applied once. Submitting the same reference again returns { "adjusted": false, "reason": "already_applied" }.