There are some troubleshooting steps that you will want to follow:
Make sure you have a stable and strong WiFi connection
Turn your device off and then back on again.
Toggle airplane mode on and then off.
Turn roaming off and then on again (this isn’t 100% necessary, but may help with connection)
Ensure VPN is off
Turn off other carriers’ SIMs (this may prevent the new eSIM from activating, as it may be fighting with the other SIM)