When you activate the Payment Services, a new menu will appear in your settings: Payment Services settings.
Collect payments for invoices delivered by email and via the platform: activate this option to add a payment button to invoices sent to customers.
Page after payment: indicate here the url to which you wish to redirect your customers once they have made the payment.
Expiry of paylink for invoices: how long your payment links will be valid after sending an invoice. The default value is 9 months.