How to get data using BLE API

We are conducting a simple test to obtain information from blood pressure devices.

Using Advanced’s Bluetooth
We are conducting a blood pressure reading test using an OMRON blood pressure monitor (HEM-7155T).

Battery information is obtained only by setting the Characteristic UUID,
Blood pressure information failed.
The error phrase is “Operation is rejected”.
How should I solve it?

Also, is there no API that sets and processes Service UUID and Characteristic UUID?

Should I use paid content?

Please reply as soon as possible.
thank you

I’m willing to bet money that that device you’re working with uses the transmit channel of Bluetooth. It’s unlikely that you’ll be able to read data from your Bluetooth cuff unless it reads and writes only to the gatt characteristic. If you’re sending data over the transmit channel, you will be unable to connect your app with your device.