Allowing your customers to come to your website to access the invoices raised by you and pay them at their convenience is a feature any business with more than 20 customers would need as they grow.
Branded Customer portal
You can get the Customer portal login link from settings -> General Settings as shown in the image below
Add the customer portal link on your website which upon clicking will redirect your customer to your branded customer portal login page. The customer can then login and access all their invoices due and pay them right away or setup autopay.
Sample branded customer portal login link - Click here