The short answer
Open Settings → Payments & messages → Direct Debit (GoCardless) and choose Connect with GoCardless. Sign in or create the merchant account on GoCardless, approve the read-write connection and return to RoundRun. Connecting does not collect any money.
After connection, use Sync Direct Debits from GoCardless. RoundRun matches existing mandates where it can and lists anything that needs a manual customer match. For a customer without a mandate, open their RoundRun customer record and choose Set up Direct Debit; the customer enters bank details on GoCardless's hosted page.
Important: syncing a mandate never back-charges an existing invoice. Open that invoice and deliberately choose Collect by Direct Debit if it should be collected.
