To process payment for the unpaid invoice kindly follow the  steps below 

Tenant will receive the login credentials to their email and hit on GO TO YOUR ACCOUNT. 

Now you will be redirected to the Sign in the page where  you can log in to your account 

Switch on to the invoice tab and choose the invoice that you would like to pay and hit on Pay Now to do payment for the due amount. If you have already added a card then simply choose the card and hit on Pay Now. 

Also you can add a new card during processing the payment. Choose New Card and fill in the card information and enable "Save this card for future transaction"

Finally you can verify the Popup message of successful payment.