What could be the possible reasons for MME rejection?

Hi Experts.

What could be the possible reason for the MME rejection?

I think you have Device Compatibility Issues.

If the device is not compatible with the network’s technology or frequency bands, it may not be able to connect to any cells in the tracking area.

This can occur when a device is used in a region where it is not supported or when it is not properly configured, also check APN setting.