In the latest update to SliQ Invoicing Online, Stripe has been added as a payment gateway for use in the client portal. By configuring Stripe, or the existing PayPal payment gateway, your customers can pay the invoices you email them in the client portal.
Stripe accepts payment online by credit card and debit card and can be set to schedule automatic transfer of funds collected into your bank account.
For more information, see Payment Gateways.