Function wait_for_balance 

pub(crate) async fn wait_for_balance<C: Currency, R: ChainValues>(
    min_balance: Balance<C>,
    max_delay: Duration,
    address: Address,
    resolver: &R,
) -> Result<(), ()>

Polls the on-chain balance of address for currency C with exponential backoff, returning Ok as soon as it reaches min_balance, or Err once the per-iteration backoff grows past max_delay.