How To Auto Pair My Ble Peripheral On My Device?

We are developing an application which needs the BLE Peripheral to be automatically paired with the smartphone when the smartphone is near the BLE Peripheral. We are using RN4871 M

Solution 1:

That a device is paired (or more correct, bonded) generally just means that the central and peripheral stores keys used for encryption etc. when they later connect.

FYI Peripherals can be programmed so that they advertise with a specific Bluetooth device address as target.

Back to your question. In Android, an "application" must initiate a connection to a device to make it connected (no matter if it's paired or not). That can either be a normal app you install or the built-in HID application in the Bluetooth stack. That said, the HID application will automatically connect to enabled bonded HID devices. So basically, if no application wants the peripheral connected, it won't stay connected.