If your order included free or discounted third-party products, their full price is deducted from the refund. This applies even when the server itself is covered by the money-back guarantee.
These products are bought from other companies at their normal price and can't be returned once they are set up.
Which products
Domain registrations
SSL certificates
Control panel licenses
How the refund is calculated
The full price of those products is subtracted from what you paid, and the rest is refunded. If their price is equal to or higher than what you paid, there is no refund.
The conditions for refunds are in How to request a refund and the Terms of Service.