@AM69: This feature requires you to be signed in to the same Samsung account on your phone and tablet, so it might be the case that your registered date of birth is restricting you from using the service. With this in mind, please connect to Wi-Fi or Mobile Data on your S10 > Swipe up from your Home Screen > Settings > Tap your profile at the top of the list > Profile Info > Date of birth > Adjust this accordingly > Save. Do the same on your tablet, then attempt to connect your devices once again.
To do this, connect your phone and tablet to the same Wi-Fi network via Settings > Connections > Wi-Fi, then swipe from the top of the screen to the bottom on both devices, and again to enlarge the Quick Panel, and select 'Call & Texts On Other Devices' from the list of options. The connection will occur automatically. Let me know if this helps.
