You can add the following code to the db/seeds.rb (or other file if have more advanced structure):
Spree::BillingIntegration::PaypalExpress.create!(
name: 'Paypal (or whatever you want)',
description: '',
active: true,
environment: Rails.env,
display_on: '',
preferred_currency: '<fill_here>',
preferred_login: '<fill_here>',
preferred_password: '<fill_here>',
preferred_signature: '<fill_here>',
preferred_review: false,
preferred_no_shipping: false,
preferred_cart_checkout: true,
preferred_allow_guest_checkout: false,
preferred_server: 'test',
preferred_test_mode: true
)
so as you can see all options are with preferred
prefix.