commerce-8.x-2.8/modules/payment_example/config/schema/commerce_payment_example.schema.yml

commerce_payment.commerce_payment_gateway.plugin.example_onsite:
  type: commerce_payment_gateway_configuration
  mapping:
    api_key:
      type: string
      label: 'API key'

commerce_payment.commerce_payment_gateway.plugin.example_offsite_redirect:
  type: commerce_payment_gateway_configuration
  mapping:
    redirect_method:
      type: string
      label: 'Redirect method'