WiFi Calling and Calling through mobile data mechanism

Hi,I m having a strange problem on my iphone 17 pro max on which i am using two sims and i am able to receive calls on primary sim if i m calling from the secondary sim through its mobile data.
However it works intermittently and not all times,also i am using a 5g router sim setup for wifi and on that also it VoWiFi works intermittently,have tried to change the DNS as well but doesn’t work.

Can someone let me know where the actual issue exists.

My secondary sim is of Jio and the 5G router setup is also of Jio.