Caterpay is a payment gateway, just like your PDQ machine.
Your PDQ machine uses a Merchant ID (a "MID") from an acquiring bank which is for face-to-face or "customer present" transactions (ie; the hotel guest enters their PIN on the terminal and this is used as the authentication).
Caterpay needs a MID that is configured for customer NOT present transactions. You don't see the guest when they offer their card details, as often they will be at home or work making the booking online or over the phone. They authenticate themselves using the CVV number (web and phone) and sometimes using a Verified by Visa or Mastercard 3D Secure one-time password on your website.
Transactions charged through your PDQ machine take up to 3-5 working days to be processed by the banking system and are then "settled" into your business bank account.
In exactly the same way, transactions charged through your Caterpay will also take up to 3-5 working days to be processed by the banking system and are then "settled" into your business bank account.
In practice, most transactions are settled overnight these days.
Before going live with Caterpay, we strongly recommend making a test transaction of a low value, eg £1.01 using your own card. You should keep an eye on your business bank account for that amount being deposited 3-5 days later.
This is important because once, a property gave us a MID where they had mixed up 2 of the numbers. Six weeks later they asked us when they would start to get their money. It had been going in to someone else's business account the whole time.
Making a test transaction before going live, and ensuring it settles in your business bank account only takes a few minutes and will highlight immediately any potential issues.