"'ExternalPurchaseCustomLink' is only available in tvOS 18.1 or newer" errors are thrown in Xcode when building a project with a Codeless IAP Button on tvOS

How to reproduce:

1. Create and open a new project
2. In the Build Profiles window, switch the platform to tvOS
3. In the Package Manager, install the “com.unity.purchasing” package
4. In the top menu, select Services > In-App Purchasing > Create IAP Button
5. Build for tvOS
6. Open the “Unity-iPhone.xcodeproj“ in Xcode
7. In Xcode, click Build
8. Observe the Xcode build status

Actual result: The build fails with ".../Libraries/com.unity.purchasing/Plugins/UnityPurchasing/iOS/SK2/ExternalPurchaseStandalone.swift:65:32 'ExternalPurchaseCustomLink' is only available in tvOS 18.1 or newer" error
Expected result: The Xcode build succeeds

Reproducible with: 5.4.1 (6000.3.17f1) (by reporter)

Reproducible environment: macOS 26.5.2 (M5) (by reporter)
Not reproducible environment: No other environments tested

Note: Not tested by the CQA