Login into FactuurSturen.nl and go to "Settings" > "Connections"

Click at the bottom of the page on "Create API key"

Enter "RCUR" as description and click on add. (make sure that active is checked)

Go back to RCUR and go to "Settings" > "Integrations"

Choose for the invoice app "FactuurSturen.nl"

Enter your FactuurSturen username and API key

Your account is now connected and the invoice features are activated