apple-app-site-association

The hosted file should have the following content:

"applinks"

"details"

"appID"

"S8QB4VV633.com.example.deeplinkCookbook"

"paths"

"*"

Set the appID value to your Flutter application ID.

Set the paths value to ["*"].
The paths field specifies the allowed universal links.
Using the asterisk, * redirects every path to the Flutter application.
If needed, change the paths value to a setting more appropriate
to your app.

Host the file at a URL that resembles the following:
<webdomain>/.well-known/apple-app-site-association

Verify that your browser can access this file.

Testing