Magento store Admin has to create a PayPal Business Account for receiving payment of in-house products sold on the website. For this Admin has to set Enable Admin Business Account to Yes from PayPal configurations and enter the Admin Business Email ID associated with the PayPal Business Account and save the configurations.
 

Goto Admin > Ced Marketplace > PayPal Onboarding and click Connect button to onboard the Magento Admin as one of the sellers on Marketplace.