To ensure the authenticity of interactions between your app and Truecaller, you need to generate an app key [ partner key ] and app link from Truecaller developer account ( https://developer.truecaller.com/login ) by adding your App Name, Bundle Id and prefix.
To generate a new app key for your iOS app, go to the 'MANAGE APPS' section on the developer account dashboard and click on 'CREATE APP'. Select 'iOS' in the App type and continue to enter your app details
You can find your App Id in the "Apple Development Portal".
If you do not have App Id yet, then open Project -> Capabilities -> Enable Associated Domains. New app id will be automatically created by Xcode.
To find the Prefix, go to the member center on https://developer.apple.com and look at "Certificates, Identifiers & Profiles", click "Identifiers", then "App IDs" in the section under "Identifiers". Find your app, click on it, and there you will be able to see the Prefix value ( Refer image below )
Once you input your app details and create the app, you will be able to see the "App Key" and "App Link" values for your app. You need to include these values in your project to authorise all the verification requests.