1. Make sure your eSIM is activated and working properly: Check with your carrier to ensure that the eSIM is activated correctly and that your data plan is active.
2. Check your iMessage settings: Make sure that iMessage is enabled and that your phone number and email address are listed correctly. Go to Settings > Messages and check the settings under "Send & Receive".
3. Restart your device: Sometimes a simple restart can fix issues with iMessage. Press and hold the power button, then slide to power off. Wait a few seconds, then press and hold the power button again to turn your device back on.
4. Reset your network settings: Go to Settings > General > Reset > Reset Network Settings. This will reset your Wi-Fi networks and passwords, cellular settings, and VPN and APN settings.
5. Update your device: Make sure that your device is running the latest version of iOS or iPadOS. Go to Settings > General > Software Update to check for updates.
If none of these steps resolve the issue, contact Apple Support for further assistance.