In order to process payments through Invoice Simple, you'll need to have a PayPal business account. If you don't have one, no problem, we make it easy to get one during the signup process.
Many people will already have a PayPal personal account, which allows you to make online payments anywhere PayPal is accepted. Such an account would usually have your banking or credit card information on file to make completing a payment faster and easier. Personal accounts are for making payments, but not for collecting payments.
PayPal business accounts allow you to collect payments and then send the funds to a connected bank account. This is why you would need a PayPal business account in order to use payment processing in Invoice Simple.