JIO 5G Not Working

Sometime it's just a matter of resetting network settings on the iPhone, using these instructions:

Settings > General > Transfer or Reset [Device] > Reset > Reset Network Settings

(bearing in mind that this procedure also resets Wi-Fi networks and passwords, cellular settings, and VPN and APN settings that you've used before).

If the issue still persists, only your cellular carrier can help you.

Regards

Giulio