If you’re unable to add your PayPal address in your Seller Settings, it’s likely that you do not have a Verified PayPal account. Discogs requires sellers to have a Verified Paypal account in order to set up a marketplace and begin selling.
Per PayPal's description, a Verified account indicates that the "seller has provided additional evidence of their identity to PayPal by passing key security checks and completing the PayPal Verification process."
To become a Verified PayPal account holder, please visit the PayPal Verification FAQ for more information.