Account access may be suspended for advertisers using Yandex units who haven't made payments for over a year. In this case, calling API methods results in the error 54, and the web interface doesn't allow access to any operations except switching to a currency.
To continue using the API, you need to switch your account to a payment currency. To do this, click “Switch now” in the Yandex.Direct web interface. For more information about switching to a currency, see the Help for Yandex.Direct: Russian rubles or other currency.