I have developed & installed an iOS app locally on my device.
And have set custom scheme in the info.plist as mydlink
Set associated domains
Experienced the same problem.
The solution for me was to use the
Identifiers -> App IDs -> 'my.app.ID' -> Prefix
You can find it on: https://developer.apple.com/account/ios/identifier/bundle
Instead of the 'DevelopmentTeam'
number from the .pbxproj
which I used and add it to the Team ID
for my iOS app in the Firebase console.
And don't forget to download and add a new .plist to the project.