SIM LOCK

You will need to contact the carrier that it is sim locked to

1. Only your carrier can unlock your iPhone. Contact them and request an unlock. After you submit the request, it might take a few days to complete. Contact your carrier to check the status of your request.

So … it didn’t “suddenly change” …

… rather you installed a new SIM which didn’t work.

Your phone is carrier-locked to JIO.

Only JIO - as the original “subsidizing carrier” - can “release” the carrier lock.

If you’re no longer JIO’s customer … you’ll likely find this to be a formidable undertaking.

How to unlock your iPhone for use with a different carrier - Apple Support

Where, exactly, did you buy the phone?

If it was sold in the US by a retailer other than Apple, it can only be activated on a US carrier and will lock to the first carrier used.

It sounds like you purchased a phone that was hacked to illegally unlock it.

If you are not a current or former customer of the US carrier it's locked to, your chances of getting it unlocked are extremely low.

The phone must be carrier-unlocked to add an additional eSIM as well.

Carriers tend to not like it when they perceive that a customer is possibly “jumping ship” … especially if it possibly violates the agreed-to terms of service re: a carrier-subsidized phone.

Regardless, your ONLY way forward with THIS device involves contacting JIO.

Then you’ll need to contact the US-based subsidizing carrier.

We have no way of knowing.

Your posts make it unclear as to how the phone was procured or who might have originally subsidized it.

Best of luck going forward.

That does not answer the question of where, exactly, it was purchased.

If it was purchased from a carrier or at a retailer such as Best Buy, Target, or Walmart, the phone was NOT sold as "unlocked".