s11s

Have not done it myself. But does not Cross Domain tracking help here?
<https://support.google.com/searchads/answer/9165554?hl=en|https://support.google.com/searchads/answer/9165554?hl=en>

Yeah you would just need to ask your web developer to create cookie for cross domain tracking. In addition you would also need to update your cookie language to include this new domain for google ads cookies. The slower way to do it would be to have an interim page where you house the form and then this form sends the information to your app form on this <http://app.domain.com|app.domain.com>

When the user signs up using outlook or Google, it will fire a conversion event in Firebase, you can integrate Firebase with Google Ads &amp; Analytics. 

<https://support.google.com/google-ads/answer/6397604?hl=en|https://support.google.com/google-ads/answer/6397604?hl=en>

So as long as the sign up happens, it does not matter if they move to another domain because the goal is to track the conversions irrespective of domain. 

To simplify you can fire event on the click but do not count it as a conversion to know how many are initiating and then Firebase signup will give you the funnel view. And can look at the cross domain tracking as well. 