Can I use Jio SIM in the second slot of my Redmi 3s Prime phone? Can I use Jio SIM in the second slot of my Redmi 3s Prime phone? The second SIM slot is a nano type SIM slot. Please clear my doubt as soon as you can.
Not all dual SIM phones have 4G + 4G support.
It is mostly 4G + 2G(or sometimes 3G).

It is not predetermined which SIM slot will be able to use the 4G bands and which won't.

Usually when a dual SIM phone is booted for the first time with two SIM cards, on the setup screen it asks the user to select which SIM card would be used for mobile data. Whichever is selected becomes the primary data SIM slot and is subsequently used for 4G LTE or 3G whichever the phone supports. The second slot in most phones either cannot use data or even if it does, cannot use the 4G or 3G bands- whichever the phone supports and the first SIM slot can use.
In case of hybrid dual SIM phones with single SIM does not arise as there is only one SIM card in use, and the device will automatically use whichever SIM slot is occupied as it's primary data SIM and will switch to 4G if available.
There is no official confirmation of Redmi 3S Prime being a 4G + 4G phone. Seeing how it is a budget phone, it is most likely 4G + 3G/2G.
If you are booting the device for the first time after inserting both the SIM cards (doesn't matter if Jio SIM is in second SIM slot, you can select the Jio SIM when prompted to select which SIM you want to use for data and it'll work.
If you inserted the Jio SIM in the second slot after having already booted the device, it probably won't work. What you have to do in this case is reset the phone, and when you see the setup screen, select the slot in which you have put the Jio SIM, and you'll be good to go.