First click Admin icon on the left sidebar of 6Storage dashboard.

On the resulting window, click Customization >> Customization Documents

Select Sale Invoice and click Submit to customize it.

On the customization window, there are various customization options. Under Footer category, click Payment Link > click the checkbox "Add Payment Link" to enable the function. Enter the required text and click Save & Preview.

The link will appear below in the future invoices.

When the tenant clicks on the payment link, they'd be redirected to the tenant login page wherein they login and make payment.