Weekly: 1–104 (so "every 104 weeks" is valid, "every 105" isn't). Monthly: 1–24 — and note this supports any value in that range, not just 1, so "every 3 months" (quarterly) and "every 6 months" (semi-annual) are both entirely valid monthly subscriptions, contrary to what you might assume from a plugin that defaults to monthly billing. Yearly: always exactly 1 — GoCardless has no concept of "every 2 years" as a single subscription; you'd need to model that as a fixed-count or manually-recreated arrangement instead. These are hard GoCardless API limits, not values the plugin invented, so there's no settings flag to raise them.