How to add money to paypal account using API

I am looking for a way to add money to PayPal account using the API. We are making a website and using PayPal Payout API, which requires only using funds in the PayPal account balance. We want to automate adding money to the account balance and then making payouts to vendors. I have reviewed the REST API and could not figure out how to "add money" to the PayPal account.