I've just taken a look at your account, it appears that GoCardless is set up. To use GoCardless, you must head into Tools > Integrations > GoCardless.
From here you can add new pre-authorisations which are an agreed amount of money that you can take payment for invoices from. The pre-auth limit currently defaults to £5,000 and can be requested from the GoCardless integration page or from directly from an invoice, please see below:
From an invoice:
From the GoCardless page:
I hope this has been helpful!