In order to make use of Google Firebase dynamic links, you need to register a URL prefix first.
Go to the Firebase Console in your browser. By opening the 'engage menu' of your Firebase project, you will find the entry 'Dynamic Links'. After accepting, that you want to use and create your first links, continue the setup.
For dynamic links to work, you will need a 'dynamic URL' which will be used for sharing later on. The format looks like this:
How a prefix is created, can be viewed here: