code: public Offer create(Integer amount, String currency, Interval.Period interval, String name, Integer trialPeriodDays) {
          ValidationUtils.validatesAmount(amount);
          ValidationUtils.validatesCurrency(currency);
          ValidationUtils.validatesIntervalPeriod(interval);
          ValidationUtils.validatesName(name);
          ValidationUtils.validatesTrialPeriodDays(trialPeriodDays);
  
          ParameterMap<String, String> params = new ParameterMap<String, String>();
          params.add("amount", String.valueOf(amount));
          params.add("currency", currency);
          params.add("interval", interval.toString());
          params.add("name", name);
          if (trialPeriodDays != null)
              params.add("trial_period_days", String.valueOf(trialPeriodDays));
  
          return RestfulUtils.create(OfferService.PATH, params, Offer.class, super.httpClient);
      }
docs: Creates an offer via the API.
  
  @param amount          Amount in cents &rsaquo; 0.
  @param currency        ISO 4217 formatted currency code.
  @param interval        Defining how often the {@link Client} should be charged.
  @param name            Your name for this offer
  @param trialPeriodDays Give it a try or charge directly. Can be <code>null</code>.
  @return {@link Offer} object with id, which represents a PAYMILL offer.