title: Firebase dynamic link default behavior if link not registered
body: <p>Is there a way to set a default behavior for dynamic links that are not "registered"</p>
  
  <p>I may allow users to share the app. It would be nice to have <a href="https://myapp.page.link/user_id_1234" rel="nofollow noreferrer">https://myapp.page.link/user_id_1234</a></p>
  
  <p>Where I have not registered user_id_1234 with the Firebase Dynamic Link console. I know I can programically create these links but i'd rather just have a "default" behavior that happens when the link is not registered.</p>
  
  <p>Is this possible?</p>
  
  <p>Optionally it would be nice to have <a href="https://myapp.page.link/default?user_id=1234" rel="nofollow noreferrer">https://myapp.page.link/default?user_id=1234</a></p>
  
  <p>But this does not seem to be working.</p>
  
  <p>Any ideas?</p>