In GoCardless, a customer can have one or more mandates (one-to-many relationships).
When a customer creates a new mandate via a Kolleno link:
If a GoCardless Customer ID exists in Kolleno, it’s reused.
If not, Kolleno creates a new GoCardless customer and stores its ID.
The GoCardless Customer ID identifies the payer, not the mandate.
If you see the wrong customer when filling in the details, understand why here. You can also view the current GoCardless customer ID for a Kolleno customer.