iMessage issues across multiple devices
On macOS 15.4.1, attempts to "Sign in to iMessage with your Apple Account" fails.
On iOS 18.4.1, all attempts to send messages are going out as SMS, even to recipients who are known to have iPhones.
Have power cycled both devices, and reinstalled macOS on the laptop, to no avail. Help!
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iPhone 13 Pro Max, iOS 18