@CraegShoumrrae: If you haven't done so already, please download the Galaxy Wearables app from the Google Play Store, and run through the connection process. Select your Galaxy Watch5, select it again, check to see that the number code on the Wearables app matches the watch, and tap connect. From here, you will need to allow permissions for the app, and check the terms and conditions. Once you've done this, tap 'Agree', 'Agree to all' or 'Next'. Follow the on-screen instructions to finish pairing the devices.
Now, on the Galaxy Wearables app, go to Mobile Networks to scan for an eligible network, and follow the prompts to complete the eSIM activation.
If you have followed the steps above, and the issue has persisted, then please reach out to your Mobile Network directly to see if they're able to shed any light on this for you.