Why sim is not supported in my phone

Hi @kanhaiyaraj

The phone may be locked to a particular mobile phone service provider and the SIM card you have inserted belongs to another provider and is not accessible.

Here's a guide¹ that shows how to choose which providers are supported by the phone that may help.

If there's only 1 provider listed then the phone is locked to that provider and you would need to contact them regarding how to unlock it so that it can be used with other providers.

¹ I realize that the guide is for a different Oppo model but generally same make phones are usually set up the same way.