You use Shopify because it is easy to use, convenient, and powerful. I agree, and get out of the way as much as possible to let you continue using all the Shopify features you are used to, opting to sprinkle in ticketing features where appropriate.
For example,
You continue to use whatever payment system you have, e.g. Shopify payments
The app creates regular products in your store, that you can treat just like any other product
The app uses fulfillment so you can track the progress of generating tickets
We integrate with your existing order confirmation emails, SMS, and check out process, as opposed to rolling our own. i.e., the app uses Shopify checkout