Invoice Simple gives you the ability to offer both Stripe and PayPal as payment options for your clients. All you need to do is connect your PayPal business account to Invoice Simple by following these instructions and create your Stripe account by following these steps. No Additional steps are required; once the accounts are connected, both options will be available to your customers.
Once both processors are set up, you'll have the option to toggle them off and on in your payment settings.
When your customers view the checkout, they will have both PayPal and Stripe as options for payment.