Secondary SIM become No Service while using Primary SIM

Hi bro I am using an iPhone 13 with 2simcards
When i am talking over the phone using the primaryline the secondary line will turn to no service. If i taking over the secondary line
Primary line goes to no service .this issue not only in 13 model, i checked with my Frd mobile he using 14 pro. He also facing the same issue.
Network : jio and airtel.

Hello bro, that is normal in Dual SIM when we use GSM Network on both or in any one SIM. if its VoLTE Network like JIo, then both network can be used at same time as per my understanding. Airtel in many areas still providing GSM Network.

I will check with the Dual SIM mode working with my friends and confirm again.

Thank you bro
But I checked with Android mobile this type of issue does not occur.
I forgot to tell you one thing.
Ex: When we call on the primary line it takes time to turn on for no service
The first 15 to 25 sec signal is slowly dropped after that it goes to no service.
But when we enabled on wifi calling I thing it’s working fine.

Yes bro. exactly. I just activated dual SIM in my phone to test this case. even in VoLTE network the second line goes offline. Seems like Dual SIM Dual Standby feature in iPhone works this way. We wont be able to receive call in the second line through call waiting when first line is activate. I tested this in iPhone 12.

In latest android phones, Dual SIM are active. I havent tested this in newer iPhone 14 models. But asked my friend to test the same and get back to me. Will bring a short video explaining how it works.