Cellular connection issues in a rebuild ipad air5

I have recently rebuilt an ipad air getting a used motherboard. The system was reset with IOS (12.1.1). It worked nicely until tried to test calling through it. I got a VoLTE sim to activate “Jio4G Voice” and first time when the sim was loaded I got “No SIM” message. Under settings also the “Mobile Data” button was inactive. The SIM tray was found not connected to the logic board! After connecting that the “No SIM” message went away and the ipad asked for the SIM lock. It took the SIM lock pin and everything appeared ok. In settings the “Mobile Data" option became active. Next LTE was enabled and Roming was set to ON. Since the software sets the APN there was no choice to set other than keeping in auto mode. In “Settings>Mobile Data” shows the network name JIO with network selection set to “Automatic”. But “Settings>General>About” shows “Network not available”. The carrier is shown as “Jio 35.0”.

I learnt for IOS 12 there is a problem with Jio 35.0 and the carrier must be set as “Jio 35.1”. This can not be set since the “carrier tab” is inactive. Going over to manual network setting has also the same problem. Jio network with ID 495866 (for Jio) is not available. Got back to factory reset again and updated ios to 12.1.3. The problem persists. Is it a network problem or there is a problem with hardware or software ? I will be very happy to get some feedback/advice . Thanks.