Two independent gates have to both pass. First, the currency has to support an instant scheme at all — currently GBP and EUR map to "Instant Bank Pay," and AUD maps to "PayTo"; every other supported currency has no instant option. Second — and this is the surprising part — availability also depends on WPDD's own Default country setting in Settings, checked against a hardcoded list of countries where GoCardless currently offers instant payments (GB, AU, DE as of this writing). That's your site's configured country, not the customer's actual bank location. If your default country is set to, say, France, the instant-payment option won't offer itself even though the currency (EUR) would otherwise support it — because GoCardless's IBP/SEPA-Instant rollout for EUR only currently covers Germany.