From my understanding, Xamarin is used more for Native Apps... Is your app Native, or has it been built as a Native App wrapper, loading in a website like app.site.com?
If it's a Native app, you need to integrate the Mobile App SDK which works very differently than web requests (you need to set up context variables, use trackState and trackAction functions, and map the context variables to your props and eVars using processing rules....https://aep-sdks.gitbook.io/docs/
If you are doing this, I highly recommend installed the AEP Assurance extension so that you can debug easier.
If you are actually loading a variant website through something like a webview within your app, then the tracking can be done like any website, and you should be able to test the web site (app.site.com directly) or see the tracking calls by connecting your device through a proxy to your computer and using an HTTP Sniffer tool like Charles or Fiddler to debug your implementation.