No, and you do not need one. Halo runs in your web browser. There is nothing to download and no account to create.
Everything you would expect an app to do happens on the web: buying a plan, installing your eSIM, checking your remaining data, topping up, and chatting with Hal. Your portal link is in your order confirmation email and opens straight to your plan.
Why there is no app
An app would be one more thing to download, sign into, and keep updated before a trip you are already packing for. The web page does the same job the moment you tap the link, on any device, with no install and no password to remember.
Add it to your home screen
If you would rather your portal page sat with everything else on your phone, add it to your home screen. It then opens full screen from its own icon.
iPhone: tap the share icon, then Add to Home Screen.
Android: tap the menu, then Add to Home screen.
Desktop: bookmark the page, or open it on your phone to add it to your home screen.
The eSIM itself is not an app
Your Halo eSIM is a carrier profile that lives in your phone’s own settings, alongside your normal SIM. Installing it does not install anything you open or launch. Once it is on your device, your phone handles it the same way it handles any other mobile line. See what is an eSIM.