If you have not been able to collect an invoice through GoCardless, you can re-launch the collection from the invoice itself.
What is the problem?
It is possible that the direct debit collection failed or you cancelled it manually, and you need to request the credit to the customer again.
How to solve it
If the direct debit failed:
Go to Sales > Invoices.
From the three-dot menu (⋮), access the edit options for the invoice with the collection set up using GoCardless.
Change the due date to a new one.
Click Save.
This will re-enable charging through GoCardless.
If you had previously cancelled the charge:
Go to Sales > Invoices.
From the three-dot menu (⋮), access the invoice editing options.
Check the Collect via GoCardless box again.
Click Save.
Once the invoice is saved with these changes, a new charge order will be generated through GoCardless.