For PayPal, there are two different flows:

• SALE: The payment is authorized and captured immediately – i.e. the shopper's funds to cover the payment are retrieved during the same transaction session.
• AUTH: The payment is first authorized; capture can occur immediately or separately, at a later time.

This error happens because PayPal is set up on the AUTH flow, while the PayPal configuration defaults to the SALE flow. This is defined by the intent configuration in PayPal's Drop-in configuration. 

In case you are integrating the AUTH flow, the intent should be set to authorize (AUTH). To solve this, set the configuration.intent to authorize when you create an instance of Drop-in. More information on this can be found here.