Get current account subscription

Returns the current plan, billing period, subscription status, trial-plan indicator and credit tiers. contactsAndEmailsTier covers both lead and email; personalizationTier, validationTier and socialActionTier cover their respective credits. plan.credits shows the base plan allowances, with lead and email grouped under contactsAndEmails; tiers show additional allowances. Both are monthly amounts, except lead which is active-contact capacity. isTrial indicates whether the account is on the trial plan, including an expired trial. nextBillingAt is the next billing date in UTC, or null when no renewal is scheduled.