Well, I would just attempt a MOC and see how it goes. If MOC is made, then it means the UE is attached and capable of doing voice calls (through VOLTE I assume ?).
Try to do the MTC after that.
If MOC is not possible, then you know for sure there’s an issue. I would investigate the ATTACH procedure (which you can trace by doing an “airplane” mode ON/OFF during the tracing)
Also, try to do packet transfers. If those are possible but not the VOLTE, then it’s something else altogether.