Using Deep links (or other) to open application via an App Launcher

I have a client who has there own build App launcher running on their iOS devices.

They wish to add my Ionic application to this. The info I have from them is

 it is just a launch platform for CompanyX apps
there are two ways to launch an external app

1. Using a universal link
2. Custom URL e.g. to launch Microsoft PowerBI we use mspbi://app/

At the moment custom URL is the preferred method so apps can be launched while offline.

At this stage I am not sure how this launcher works underneath, and am not sure what to ask?

From what I can see, I should be able to use the the Deep Links plugin for this?

It is not being open from a web site, so not 100% sure how I would configure this (I don’t want any url tied to a single web site address, as I want any client to be able to use this)

Can I use something like…
I have seen an example like the following…

ionic cordova plugin add ionic-plugin-deeplinks --variable URL_SCHEME=myapp --variable DEEPLINK_SCHEME=https --variable

But in my case, what would I use for the DEEPLINK_HOST? Can this just be anything

Thanks in advance for any help!